There is certainly a hierarchy of quality, mainly related, as Morris stated, to TDP compliance. The odds are that most of the mass-produced rifles will run fine in the hands of most people. The higher-end rifles (Colt, LMT, Daniel Defense, Noveske, and BCM) ARE indeed built to a higher standard and are more likely to hold up. Some of the things that the lower-end companies are not doing or not doing well are significant and can have an impact on reliability. Carrier key staking, high pressure testing and magnetic particle inspection, etc are all very important. Better QC is better QC and can less QC can only be subsidized so far by price.
It's hard to make a clear analogy to the handgun, automotive, or tool world (or anything else guy-related) that doesn't evoke a bunch of brand-warring, but I guess to me it's the difference between a Mac or Snap-On wrench and a craftsman or Ridgid one, or the difference between a Beretta 92 and a Taurus PT92. Both items will probably serve most folks well, but one of them is truly "professional grade" while the other will almost always be considered "as good as."