for my arguement, i will use 2 other games as references, diablo 2 and ultima online. i have played both of these games extensively and understand just why the need for more character slots is eminent.
in diablo 2, you have the ability to create an account regardless of how many you created before it. on each account you can create 8 characters. this is not a problem and shouldn't be for anyone because you can create as many characters as you possibly can without any hassle.
in ultima online, you can create 5 characters, per shard. (or server, save Siege Perilous, which you can only have 1) this is really not a problem either, because with as many skills as the game has you also have much flexibility as to how you can play your character. you can basically change anything at any moment, free of hassle. (except skillgain, that's a bitch)
the problem in guild wars is that you are limited to 2 skill classes and have no flexibility. some might say that i have the ability to change my secondary profession in the crystal desert, but i will retort with: is it the same to play a e/mo as a mo/e?
with 30 different (PvE, 36 PvP) combinations i definitely need more character slots. right now, i have a Mo/W, W/Mo, E/Mo, and my pvp character (which i will never use as a PvE slot simply because i don't like being locked into the limitation that is PvE, yes, don't get into that with me please). i am itching to delete my w/mo to make a ranger but i have about 45 hours on her and i don't feel like losing all of that time. so what i must do is gain skill points on my monk and unlock skills by changing my secondary profession. i have always seen this 4 character deal as a design flaw waiting to be patched and i would like to see it in a patch soon, if not, then in chapter 2.
B


I'm sure other people would as well. Sure they'd have to store more things on their servers, but that extra bit would be there regardless of whether a current player bought a copy or a new player bought a copy.