Magic-users, or mages (as they were called in 2nd edition), have always been a staple of Dungeons & Dragons, or any other fantasy RPG. Although their selection of spells has changed a bit throughout the editions, I wonder about their weapon selection a bit (from Unearthed Arcana):
Caltrops, daggers, darts, knives, slings, staves
In 3e, wizards were given the following weapons:
Club, dagger, heavy crossbow, light crossbow, quarterstaff
Unlike clerics or druids, whose limited weapon selection derives from religious views, magic-users have no real reason to avoid weapons like swords, spears, or maces. One reason for limiting their weapons selection might be to limit them to only simple weapons that can be learned easily, but of the weapons listed above, the staff is most definitely not a simple weapon at all, as I have been finding out through personal experience recently!
Any weapon requires some proficiency to be able to use it to kill someone; further, any weapon requires much more proficiency to be able to use it to attack, defend, and parry other weapons skillfully. I would not expect a magic-user to be able to do much with any weapon at the latter level, but some weapons require quite a lot of time to be able to be used at even the former level.
A sword, for example, can be quite heavy, but is rather simple to use in a lethal manner, even for a magic-user (as long as he has the requisite strength to lift it fairly easily). A blunt club is fairly simple to use as well, even though it lacks a blade. However, the long staff is a rather complex weapon that is hard to use in a lethal manner due to its great size and special manner of wielding (i.e. with two hands at different parts of the pole). With skill, the staff can be a very potent weapon, using both ends to attack and defend, by poking, swinging, and blocking; however, without skill, a staff is very hard to use at all.
Thus, although magic-users are often thought of as staff-toting old men, I think that learning to use a staff well would take days and days of training - something that they would probably prefer to spend in the old, musty tower, reading magic tomes.
Perhaps a better list of simple weapons would be:
Caltrops, daggers, darts, sling, crossbow, spear, club, mace, short sword, hand axe, hammer, short bow.
A few heavier weapons are simple as well, and so perhaps a magic-user with STR 13 or more could also use:
Long sword, bastard sword, footman's mace, morningstar, battle axe, staff sling.
Of course, there is nothing wrong with a magic-user using a staff as a walking stick!