While I don't share Ranger REG's intention of quitting when 4e came out, I do understand it.
I will play RPGs for as long as I continue to enjoy them, and as long as I can find a group of others to play with, and with whom I can spend time comfortably. (I don't necessarily require that the people I play with be my friends outwith the game, but I do need to be able to spend time with them without wanting to punch them in the head.) As soon as RPGs fail one of those two criteria, I will quit, and not look back.
I personally thought that 3.5e was an improvement over 3.0e. Additionally, with the amount of use I get out of the core rules, I didn't really object to having to invest in a new set. So, I wasn't offended or disillusioned by that release. However, if WotC were to do something that really did offend me (such as a 'rulebook' explicitly attacking my religion - something they wouldn't actually do, but I needed an example), then that would probably sour me on the game. At which point, yes, I would walk away. (Of course, I'd probably just move to another system, but I can well understand others not doing that.)