Really, here's the difference as I see it. There are three visions of a low-level wizard:
1. The wizard has almost no magic. He can fire a crossbow or throw darts as well as a member of the town militia, and he can create one or two magical effects a day.
2. The wizard can create a variety of minor harmless magical effects at will, can create one or two more involved magical effects per day, and he can fire a crossbow or throw darts as well as a member of the town militia.
3. The wizard can create a variety of minor magical effects at will, some of which can even do damage that comes close to the deadliness of a town militiaman. He can also create one or two more involved magical effects per day. Because he relies on magic, he may not even carry a weapon other than a ceremonial dagger.