The fact that you NEED a good guild to get the best gear makes you feel 'needed' by the guild. It makes you feel like you are contributing to the guild's success by helping them raid, which builds the comradery that MMOs are all about. If solo players could do just as well, there would be no benefit to working with others, and thus no point to being in a guild other than the social aspect.
Having said that, I can see for pure solo players it's frustrating that in most mmos, once you hit max level, you are DONE. You cannot progress anymore period. I guess they could put in some solo content after that so you could improve your gear (solo versions of all the raids?), but it would HAVE to be substantially slower/more limited than grouping for reasons stated above.
Why are you guys so opposed to pugging? Now that Wow has cross server queuing for instances, it's basically wait 5 mins for group, do one wing of dungeon for 20 mins, and you're done. You don't need to be hardcore to do that. You're not even obligated to stay for the whole thing anymore, since if you leave half way through your group can easily find a replacement via the dungeon finder.
As for buying gear via micro-transactions, what if you buy the best gear in the game? What do you do then? You've basically finished the game at that point. PVE is all about grinding for phat l00tz and if there's no more loot to get, there's no more reason to play the game. That's like getting a single player game and buying a cheat code that gets you to the ending credits. The only reason I can see for micro-transactions is if you DO want to play with others, but your friends/guild are too far ahead and you need to catch up.