Queens Gambit Declined vs Slav: Exchange Variations I am a keen player of d4 as white. One of the things that I often read is that the exchange variation of the Queens Gambit Declined is generally considered good for white:

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1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. cxd5 exd5


But the exchange variation of the Slav (or exchanging after Nc3 in the Slav) is considered better for black:

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1. d4 d5 2. c4 c6 3.cxd5 (3. Nc3 Nf6 4. cxd5 cxd5) 3...cxd5


I checked http://www.chessgames.com/perl/explorer and it seems to support this view, with the following win/draw/lose statistics for white for the above variations:


QGD All Variations: (41%, 37.7%,21.3%)
QGD Exchange:  (49.8%,35.3%,14.9%)
Slav All Variations: (37.8%, 41.3%, 20.9%) 
Slav (early exchange): (22.5%,55.2%,22.3%)
Slav (exchange after Nc3): (30.2%,49.9%,19.9%)


So it seems clear that the exchange of central pawns favours white in the QGD, but favours black in the Slav.

My question is simply - why? The resulting positions are superfluously similar (in the Slav black is missing the c-pawn, while in the QGD the e-pawn), yet positionally these must be very different! Is there a simple explanation of why this is the case? Would a clever newbie (i.e. somebody who plays chess very well, but have never played these variations) be able to make this deduction over the board through pure reasoning, or is this the type of thing you can only deduce by studying the opening theory?
White happens to have a couple of nice concrete plans in the particular QGD Exchange variation you mention (1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.cxd5 exd5). One involves e3, f3, Nge2, and a break in the center with e4. The other is a minority attack on Black's a7-b7-c6-d5 pawn structure with b2-b4-b5. You will note that White's stats are much worse in the variation 1.d4 d5 2.c4 e6 3.Nf3 Nf6 4.cxd5 exd5, even though the pawn structures are the same, because he no longer has the f3/e4 plan. So it is not nearly as simple as "the exchange of pawns favors White in the QGD but favors Black in the Slav."