Wait a second, this is a little different than your typical situation with something you purchased.
They've set MANY of these expansions up to where if you DON'T upgrade, you'll be left behind. They entice you by adding items to the game and creating new features that can only be used if you purchase the expansion, and they even have been known to intentionally make things temporarily more 'appealing' (better experience gain, insanely awesome item drops) for the first few days to generate enough buzz where everyone else finally says 'fek-it, I'll go get it'. Then, after they've met some expectations, the nerfs are incoming. Everyone is then back to bitter and pissed again.
This isn't saying they shouldn't release expansions...it's just the way they shove it down your throat. If you play EQ, you know for the past several months you've had to cancel off their nonstop advertising for this expansion. If enough people 'shift' to the new areas in this expansion, others have no choice but to follow, since you are pretty much dependent on your peers as you reach the higher levels and what you might feel is nearing "endgame".
Don't diss people for being pissed...Sony has sh*t on their subscribers far too many times for people to happily just throw more money in their direction. Most are going to pay for it, but they aren't happy to do it. This isn't a case of The Sims where you can play your original game without the expansions and be just fine. You don't keep paying up with these guys, and you'll find your character's progression hurt by it. That's where it's wrong.