Why dxc6, not bxc6?

We're told to control the center, but most often after a Bishop captures a Knight on e.g. c6, it seems GM's tend to recapture with the d-pawn, and not the b-pawn. Like in this example, of the Ruy Lopez: Exchange Variation. 

I'm sure there is a reason for this. Can anyone explain, please? 

What does that explain? 

It's a named opening

http://www.chess.com/opening/eco/C68_Spanish_Game_Exchange_Variation_Lutikov_Variation

Ah! And then Bg4. Then it makes sense. 

Yes, it's a named opening. That doesn't explain anything. I guess dxc6 is better for two reasons: the open d-file, and the possible Bishop pin. Right?

doesn't that mean that Nxe5 is a bad move???

I think it's an interesting question. Generally, the principle is to recapture toward the center.

The dxc6 is one of the two exchanges that gives white it's main advantage in the Exchange Variation, a winning pawn end game. It's a winning end game because after the second exchange, white has a pawn majority on the king side and should be able to promote with only pawn moves (all else equal, as they say). Black gets a queen side majority but it is compromised (crippled) with the doubled pawns. It means white can hold off promotion with just three pawns. I think a Stonewall type configuration is mentioned by Soltis but I've seen another procedure in a pawn ending book.

By the by, there are two exchange variations, the one used by Lasker and the one made popular by Fischer (castling before the second exchange). There are a lot of cool implications resulting from Fischer's move order.

When I've run a few computer simulations, I'm not sure the computer has read Soltis's book. It seems to use a different "plan."

Kmoch's writing is unclear to me. He seems to argue for bxc6 to avoid giving up the pawn majority but acknowledges the text move is dxc6 as per Lasker. He acknowledged, Lasker was generally successful with this opening.

The problem with bxc6 is in the comparison with dxc6 in terms of piece play rather than pawn play. Even if white could take the e pawn, black's queen can pin white's pawn and knight, regaining the pawn and some position. Playing bxc6 removes this good option for black....and yes, dxc6 opens diagonals.

I'm not that experienced but from the games I've played, bxc6 gives black many more opportunities to screw up. The main idea is for white to push the d pawn for the second exchange. It creates good pinning opportunities if black does bxc6.

That's my take on it at this point. I'm eager to hear some insights and corrections.

Generally, white win't respond by playing Nxe5 because that move is too greedy in the opening.  (All you pawn grabbers out there remember this principle: Never grab pawns in the opening unless your opponent offers a gambit--in which case you can still decline it.  It is much better to concentrate on developing pieces in the opening)  Here's something else which may happen:

Nice explanation, MyCows.... 

And an interesting little example, Hrolf. 

Thanks to all of you, I got my question answered. These forums can be really good. 

Here's another wicked example, between players rated above 2200, and lasting just 10 moves. 

One wonders how White made 2329 playing crap like that. 

Seriously, that looks like a fixed game to me.

to cigoL's post,

The mating pattern in the game you posted is called the Fishing Pole Trap (typically, you sac the knight instead of the bishop, but other than that, it's about the same)

Thank you for the post.

I came here googling "dxc6 or bxc6" when encountered it in a game, because wanted to learn the logic behind either of the moves.

So here is what just happened. Thank you for the forums, I learnt something new.