What's the problem with 5. Nxe5 in Spanish Exchange? Spanish exchange: http://en.wikipedia.org/wiki/Ruy_Lopez,_Exchange_Variation

Using the image in the Wiki page, after 4 ... dxc6, why can't white just respond by Nxe5, thereby gaining advantage by having one more pawn?  None of the books / articles I have read has ever even discussed this move...
After 5. Nxe5, black has two ways to recover the pawn.

The first is 5... Qd4, forking the knight on e5 and the pawn on e4. White cannot defend both so has to move his knight, after which black takes on e4 with check and has a fine game.

The second is 5... Qg5, forking the knight on e5 and the pawn on g2. White again has to move his knight, leaving black free to take on g2 and gain a tempo attacking white's rook.