99% of the ar15 rifles available today are perfectly fine for 99% of the people buying them.
This is true for the majority of internet gun discussions, to be honest. Which gun/brand is most accurate, which gun/brand is toughest, etc, all boil down to the fact that most firearms users in the United States today do not get "rode hard and put away wet", and thus most firearms produced today fit that bill really well.
There are a lot of discussions that amplify the differences in that remaining 1% and make it look like there are issues a lot more significant than they really are in the grand scheme of things.
For the AR-15 crowd, you also have to remember that on top of the normal sporting American firearms owners, there are also a good number of LEOs, security contractors, etc who use privately-owned AR rifles as duty weapons -- a number that pushes the 1% number above to some larger number (I don't know what it is, though) Those people actually do need a rifle that can stand abuse on a harsh duty schedule.
Add to it the number of 'tactical' types who don't actually have a need for such a rugged firearm but, for whatever reason,
think they do, and now you have the makings of serious internet discussion.
All that being said, here's a pretty interesting thread from AR15.com where a "carbine course" instructor (this gentleman: Pat Rogers --
http://www.eagtactical.com/abouteag.asp) discusses his observations about the weapons he's seen used at his classes. He's not a brand snob, but has definitely seen trends in what brands work well
in his environment and which ones tend to have problems -- problems that likely wouldn't be life-and-death to that 99% of sporting AR shooters, but would be VERY critical for someone with a heavy use duty weapon.
http://www.ar15.com/forums/t_3_118/360169_What_Parts_Break_in_a_Carbine_Course_.html
I think it's the heavy mixing of the "duty use" crowd, the "tacti-cool" crowd, and the "sporting" crowd which causes a lot of the brand snobbery in the AR world. For some people it matters, and for some it doesn't.