We've all heard how important it is in chess to capture the "middleboard" area early in the game, to enable easy movement of troops, right?

Well, here's a game where white's pieces are all resting snugly nside their fortress. What follows is a massacre, with white's 'a' and 'h' pawns playing major roles. 

Ok makes sense. I think. 0_0

I think most of this was very poor play by your opponent; for instance, 5...b5? losing a pawn for no reason and 6...Bb6?? losing the exchange for no compensation. He was already down material but this was probably drawable were it not for these two blunders. His 2nd rank invasion may have even been winning had he chosen to actually take some of the pawns that were vulnerable on the Queenside.

To Steevmartuns....could you please elucidate on your last line, ie provide the actual moves? 

Always happy to learn!

Sure.

5... b5 is a blunder

6... Bb6 is a blunder

8. Kg2 would have been better I think

What good would 8.Kg2 have done? Defended the f-pawn better?

The King should be centralized in the endgame, so moving him towards the corner is not a good idea.

This is correct

The endgame isn't slightly better for black. In endgames with reduced material like these, it's either "white wins", "draw" or "black wins". There is no such thing as "white has an advantage" or "black has a slight advantage" in a similar endgame.

The game ends in a draw unless one of both players plays extremely badly.