IMO if the player throws a hissy fit over not being able to play something, then either they're narrow minded and only play one thing, or they're just being a jerk and trying to come up with any and all excuses to show how 4E is badwrongfun.
If the DM wants to force a game that doesn't cater to the player's preference down their throats, then he's the one being a jerk. If a player has the most fun playing a gnome bard, why try to force him to change?
Is this somehow badwrongfun, to prefer some character concpets to others? Is it badwrongfun to play something one likes, instead of something one likes less?