delayed acceptance of queen's gambit

i recently encountered such black's behaviour: 1.d4 d5 2.c4 e6 3.Nc3 dxc4. I understand it must surely be worse than the just QGA as i cant find it anywhere. But I dont understand why. All I managed to find is this: http://books.google.pl/books?id=rWYK2rOi8dAC&printsec=frontcover&source=gbs_navlinks_s#v=onepage&q=&f=false
page 32, where the author states that further delay is unsound again with no explanation.

4. e4 and white has the classical player's dream. There's still a game to play but which side would you rather be on?

But it also can be met with the normal way of accepting the gambit: 1.d4 d5 2.c4 dxc4 3.e4 and still QGA is considered sound for black (according to wikipedia). So what is the difference between the two (or even three, there's also the one from Steinitz-Zukertort).

In reply to 3. e4: 3...e5 does not lose a tempo - in the open position that arises a tempo does matter. Again - much play - but part of being a successful player is to avoid positions that decrease your possibilities. (You might be able to draw a game sometimes the exchange down but would you want to face that all the time? You have to weigh what you get versus what you lose - black is not gaining much by delaying the acceptance of the queen's gambit - in fact he loses some flexibility to meet the most aggressive e4 line and accepts a defensive stance with less counter-play.)

Pardon my illiteracy!

Paul