Personally, I agree with some of the above about when the plate jacks with the positioning, or even removal of the rear sight. But other than that I think the manufacturers are doing exactly the right thing by including them on most models.
If they don't, they have missed sales to those who want it. Those folks will NOT be happy and they will complain about it. The only happy people in this option are those who like to find something to complain about. They are always happy because they can ALWAYS find something to complain about.
If they DO include it, they will miss out on (IMO) far fewer sales to people who will not buy it primarily because it has a plate. That group will be unhappy, but I really believe this is a very small group. Those who want it and those who don't mind it are happy. Those who like to complain, will complain... so ultimately they are happy too! WIN WIN!
So including it makes a lot of folks happy. Those who want it, and those who like to complain!
If they have to tool up to support two different manufacturing / assembly processes for the two different models, that adds cost, and the price goes up on both! Guess what... we will complain about that!
If the dealer has to stock both versions at all times it increases his overhead and prices may or may not go up. Either way, if he has one and is out of the other then most customers are going to want the one he doesn't have. Again... the complainers win!
It is a TOOL. I carried an MOS since shortly after they came out. It was carried in the open, rained on, spit on, snowed on, almost puked on once, and muddy ditch dipped more than once. It never gave me any issues and I only took it off to clean under it a couple of times. Never found anything under there but dang did I ever COMPLAIN about the extra 2 minutes it added to my mud removal session.
Geez.... I gotta stop complaining like this.