The Advantage 3P has over 4.0 is that if you don't like the extra stat bonuses given to each Race, either don't use them or adjust your points buy system. If you don't like the skill max ranks idea, use skill points, etc. etc.
The point is, is that its Alpha... YOU get to try it out and have a say in its development. YOU get to pick and choose which bits you like and dislike and ALL of it is compatible with ALL your current books, adventures etc. even if it does require a little tweaking
Whereas 4.0 is ONLY a money spinning deal for WotC.
Anyone with a load of material for Greyhawk, Forgotten Realms or Eberron can still use everything they have with 3P. In 4.0 unless you live 70000 years [I'm looking at you, Elf!!] all the NPC that are, say, Human will be dead, useless, and the game world will be out of date too, and they'll want you to buy all that again as well!
3P is about you, its about me and its about us, yeah WotC, remember us? well you should do as you've already got a load of our money....*^$*ers!
4.0 sucks because it need to attract 11 year olds, it will be over simplified and all about emptying your wallet.