Well, Wizards ARE ranged, which means they'll do quite well if they're played right.
As for tanks and more DPS-made classes, they'll do just as fine if they have good armor/STR and DPS. Of course it'll be a more dull fight and a lot of melee, but that's how it is. It doesn't mean it's necessarily easier to be a Wizard. Barbs are made to deal the damage, Wizards aren't. So obviously, they /have/ to be all over the place to survive, especially in Hell and up.
Barbs and DHs probably do more damage at the spot than Wizards do ranged. Wizards are meant to delay them so melee classes take less damage and have it easier when tanking. /capt'n obvious