Comparing bass out of front speakers, which are usually in less than stellar baffles (doors) to rear speakers is a loser bet...the rears, usually in bigger, better sealed areas (like a trunk) will almost always win. And they are usually bigger.

Pull the door panel off...see all those holes? Anytime sound can get from the back of the speaker to the front, bass will suffer from the cancellation (rear wave is out of phase with the front). Same problem you get when one speaker is out of phase. Get some dynamat or something similar, seal all the holes, and the bass will improve.

Also, factory crap speakers often sound 'bassier' to a point, because they are made of cheaper, lighter material, that makes them more efficient.

Toby