Mustrum_Ridcully
Legend
I don't think 4E is incomplete if it lacks rules for firearms.This attitude comes up a lot as a defense for the things missing for 4E. In the former case, 4E is supposed to be introductory, and as such the idea that people should just "make stuff" up is a little disingenuos. New gamers aren't necessarily goin to have the exposure necessary to realize they can swing wide of the core game and still be "doing it right". The inclusion of little incongruous elements goes a long way toward giving tem that confidence. i know that the Gamma World/Boot Hill sections in the 1E DMG opened my eyes as a 14 year old, after 4 years of playing BECMI as pretty much "straight fantasy".
In the latter case: well, core games should be complete.

I sometimes wonder if it wouldn't have been better if WotC had an extra year of development for 4E, so they could create even more material and more subsystems that might make the game more "universal". But I suppose the realities of the economy make this impossible. Design & Development costs money, and if your designers are busy with 4E, they can't produce suppmements for 3E to keep your money coming in.
But what I applaud the designers for is that they didn't give us any half-finished subsystems that needed more development. Statistics for one firearm and for one laser rifle are not enough to give us a complete feeling for such kinds of weapons. You would really want more - rules for automatic firearms, reloading, ammunition. Look at the firearm rules in the 3E DMG and compare them to the rules in d20 Modern! There is barely a connection. If you really wanted to include firearms in your game, you need more than just statistics for one or two weapons.
The disadvantage of this approach of course is that
1) Beginners might not even get the idea that such things are "possible" in their game (and that can shape their perception on later rulebooks that introduce such weapons)
2) Experienced players could use these statistics as a basis and develop their own rules to complete the game. Now, they really have to start from 0. (But maybe that's not that bad? d20 Modern firearms don't really resemble DMG 3E firearms)