A couple of locked threads really have a good basis for a point to be made, but of course threads like that tend to take a nose dive quickly and end up locked and for good reason. Having said that I will attempt to give a rational way of looking at this weapon platform in regards to quality. These same things might be applied to other weapon systems.
First we should be aware of a few key terms and their definitions and why they might be important to this weapon. Such as Mil-Spec, TDP etc...First off we need to understand the need for these standards as standardization benefits commonality amongst parts, makers, reliability and costs. These standards are set forth by the US Dept of Defense. Keeping this in mind here are a few key terms....
Short for "Military Specification". This term is related to the actual quality or standards for materials purchased and used. This is not an overall build standard, just a materials standard.
Short for Defense Standard. This would be what outlines specific differences in engineering and technical requirements for military unique items or alterations to commercial designs, processes, procedures, standards etc...This would include standards for design, manufacturing, practices/procedures and testing standards.
Short for Performance Specification. This is a Performance Specification that an item is expected to achieve under specific use and conditions. This spec does not provide for the manner of testing to be used, just the end goal to be achieved.
Short for Detail Specification. This encompasses all design requirements including materials used, processes, including fabrication or construction / assembly. This may also be inclusive of performance specifications.
Short for Technical Data Package. Or more correctly "MIL-HDBK"
which is the military handbook that will encompass all of the above in regards to any item produced for the military.
Now we all understand that "if its good enough for the government" isn't always a good thing. I will also note that the above mentioned standards or "TDP" is a baseline or minimal set of standards that need to be followed. There is nothing saying that this is the absolute best standard as you can get materials, testing and build standards that may exceed these military standards.
Here is the uniqueness with the M16/M4/AR platform of weapon, but is not just exclusive to this weapon. It is known and accepted by not only the Government and military, but also civilian engineering experts in the firearms industry also agree that there are certain specific areas on this platform of weapon that should be addressed to ensure maximum reliability, even under the most extreme uses. This includes materials, testing process, build techniques, and quality assurance. This does not guarantee that every single item will not fail, or that a lemon won't get out the door, but it will very much cut down the likelihood of producing a sub-standard final product that ends up in the end users hands.
Having said all of the above, either you make a rifle that would meet or exceed Military Specifications under the Technical Data Package for this weapon system, or you don't. Of course only those supplying weapons under contract and under the scrutiny of gov inspectors can actually ever be considered a rifle built to military specifications under the correct TDP. If an item has NOT been tested and produced under military contract it is NOT MIL-SPEC. This does not mean that a company cannot use the same materials and conduct their own testing in the same manner as the government, but it is not truly MIL-SPEC. It may meet similar standards, but to truly be MIL-SPEC, it needs to be under Gov contract and go under Gov inspections.
You have some manufacturers who take the time, effort and invest the money on quality materials, quality build process, quality testing and quality quality control. They often spend the money on replicating building rifles along the guidelines of the TDP (commonly referred to as Mil-SPEC). They undeniably produce a high quality product that will withstand more harsh use and there will be less chance for failure. Again there are still going to be issues, but far far less and often much less severe of problems.
Now there are other manufacturers who might use very good quality materials with decent build standards and have good quality control and they would make a very good rifle also. But they would clearly not have the likelihood of building as good of a rifle as the above manufacturers who build towards the Govs TDP standard. However these rifles will more than likely give a shooter a lifetime of great shooting pleasure.
Next you have those, who would chose the least desirable materials and pay little attention to quality build standards. No one is saying that their rifles are going to fall apart when you take it out of the box, however the odds of getting a really bad rifle is exponentially higher than the above manufacturers. Not saying you can't upgrade these rifles to make them reliable because usually you can. It doesn't take much effort, but the companies chose to cut costs and keep profit margins high at the expense of the consumer. Or they just produce an crap rifle, that looks like window dressing trying to hawk their goods to the uniformed who couldn't tell a good rifle from a bad one. In either case this last category of rifle / weapon maker is slimy and should be avoided anyway.
Finally, why should any company produce a product with parts that is lesser in quality, build to a lower standard, not pay to have their parts tested and allow for more products to get out the door that have issues, yet charge just as much or more than the other guys? Which is exactly what you are seeing right now in this industry. I don't care if I don't need a Corvette when a Neon will get me from A-Z. If the damn Vette is the same price as the Neon, I know which one I am buying every time.
That is my opinion anyway.
See and I didn't even mention the "Cha.."