Well, actually you can still throw eggs in the air, and then DJ. Holding the Up on the analog stick while in the air. Small sacrifice to be able to DR with ease.
I tried throwing eggs with tap on and found quite a few problems.
First, you either don't have total control of your eggs or cannot DI properly when throwing them. say I just knocked out my opponent to the far side of the stage and i want to run and egg him. with tap off id be able to do it with ease. I would run, jump, throw and egg by tilting my control stick diagonally and upwards, keeping the same forward momentum of my jump and having enough control of my eggs to hit him. with tap on, you'd run forward and as soon as you'd jump, you'd stop your forward momentum in the air trying to tilt your control stick up but not too much so that you would not lose your 2nd jump. This would completely stop you in the air.....but hey, you're throwing an egg.
2nd. If you are using your control stick for jumping and throwing an egg, how the hell do you short hop egg? you would need flick your control stick, and tilt it again for your egg....again completely destroying any aerial momentum and making it extremely hard to pull of.
3rd. tell me you can throw an egg completely upwards (by tilting back) and not lose your double jump.....its almost impossible.
4th. less suicides, more egg control. (=P just added that for the heck of it)