Question on Alapin from a newbie?

I'm a beginner and I'm trying to stick to some simpler openings where I don't have to recall a lot of book moves. I know I want to focus more on end game study, tactics, etc, but I'd like to know enough of the openings so I'm not quickly in a really bad spot 5 moves into some games.

From some searching these forums I've heard a few mention the Alapin variation is good for a beginner on white after black plays c5. I decided to look at some variations in the opening explorer and when I follow some of the most common moves, the following position arises. 

My question is, why now is white willing to give up the pawn on c3 after d4xc3? Is it because of the tempo and positional advantage he now has? I'd be afraid, being a newbie, that I'd probably not adequately leverage my positional advantage as well as I should, so being down that pawn might be a pretty bad thing? Maybe I should just roll with it anyway so I learn?

Obviously for someone experienced, losing that pawn isn't a big deal and when I put it into scid and run the analysis the advantage is still to white after taking back with the knight. 

(Position below  http://www.chess.com/explorer/index.html?id=402324&ply=13&black=0 )

The Sam Collins book says the development advantage by White, control over d6 and the fact that even after Nxc3 g6 (freeing one bishop),  Black's c8 bishop still can't be freed easily make this line a risky proposition for Black.

Needless to say, White must be decently skilled enough to do something with this advantage ... just as a Gambit player would play actively and go for the throat on each move.  

Most strong players probably do this as White in this line which is why Black doesn't play this.

rick, if you notice, White has a lot of wins in the dxc lines.  There are many gambits in this fashion on both sides of the board, where the c-pawn is sacked to bring out the knight.  You might also look at the Half-Danish (1. e4 e5 2. d4 exd 3. c3 dxc 4. Nxc3) or the Scotch Gambit (1. e4 e5 2. Nf3 Nc6 3. d4 exd 4. Bc4 following up with c3).  I think your fears may subside if you study the opening a bit.  Material is good, tempos are good too, and sometimes giving a pawn away gives you the tempo you need to launch a strong attack.  

I don't think it was stated explicity in the Collins quote, but in most of these gambit lines -- especially at the club level -- you end up with white on a pretty quick kinghunt, with black falling back on defensive resources until he can defuse the position.  In those games, the Nf6 knight plays a very important defensive role.  And in this line, that knight is AWOL.

It behooves black to take the game down quieter, more positional channels.  That's why you almost invariably see ...d5 here instead.