The sunset was added, unless I am mistaken, as a "compromise", because the bill didn't have enough momentum to make it through in the first place. I don't think those that pushed the original bill, sans sunset provision, were interested in a "test-drive" to see if it did anything.
Expect to see bogus statistics when 2004 rolls around, but that won't be the primary strategy to get it re-passed and made permenant. Remember that a law with a name like the "Assault Weapons Ban" is passed primarily on emotional appeal. It's the sensationalistic nature of the bill that gives it its success, and when even Charleton Heston says "AK-47s are inappropriate for private ownership, of course" how much is supposed to get done? It's in the same vein as the ".50 [/i]Sniper[i] Rifle Ban" that've been attempted at various levels.
If it was the "Prominent Pistol Grip, Folding Stock, and Full-Capacity Magazine Acquisition Prevention Act," odds are it would not have been as successful. Instead, it's the "Crime Bill," or the "Save our Hard-Working Police" Bill, or the "Mother Theresa Commemorative Memorial Welfare Reform Bill," or my personal favorite, the "Patriot Act."
Does anyone remember when this tradition of giving laws sappy or emotionally charged names began?
EDITED TO: Respond to the previous post - The way I see it, the best policy would be to destroy the "assault weapon" myth. I can't see a better or more effective way to get public support for letting the bill die and keeping it dead.