The Ruger or the Remington are not built by a company that specializes in lookalike airguns, either. The Colt in particular, offers to void the warranty if you take it down beyond opening the action to adjust the spring tension for the bolt. But at least they provide a parts breakdown in the manual.
http://www.colt22rimfire.com/uploads/pdfs/Manual-Colt-22-TacticalRimfire.pdf
http://www.smith-wesson.com/wcsstore/SmWesson2/upload/other/S&W_M&P_1522_Rifle_Manual.pdf
The Ruger looks and handles less like a AR than the Colt or the S&W, but the innards have a history dating back to 1964 or so, so you can pretty much bet that you will be able to get parts for it in 20 years, if that matters.
The Remington is supposedly more accurate than the Ruger, but has a smaller group of accessories available on the aftermarket. Stuff like mags, barrels etc. Some for Remington, a lot more for Ruger, pretty much none for the others. Granted, the others are newer on the market, and are not built to get more than exterior dress-up accessories, though.
Invite a S&W owner out gopher shooting! Or shooting at the gravel pit, or out in the boonies. The Ruger and Remington are both able to be shot legally, at places OTHER than a Restricted Approved range. That makes them both a better choice for me.
Personal choice for me is a Ruger. Mags are on hand, Know the insides, know the mechanics, know the availability of pimp gear for it, happy with the accuracy. I can shoot it anywhere, instead of just at a range. Still trying to figure out if I'll buy a SR-22, or a kit to build one like I want, whether its the machined Nordic kit, or the molded plastic Archangel kit.
Cheers
Trev