I would guess that at top level play ... a one-pawn material difference makes a big difference in winning potential. But, fwiw, as only a 1325 rated (or so) player ... I had the same question.
@dlcurtis ... but, this post is so old ( surprised no one has answered yet), have you come up with other thoughts ?
Actually, Silman uses the example to show that e5 was NOT important. The importance of e5, if the OP had read beyond the top half of page 4 in The Amateur's Mind, is explained by Silman in that it gives White a spatial advantage. It's also clear if the WP there is left alone, it takes Black's KB out of the game and if that KB moves to become active, f6 is a killer location for a WN's outpost. But Silman points out that if White spends his time defending e5, he won't have time to do take advantage of his spatial development so he should take a look at his lead in development and see if that can give him enough initiative. Silman then goes on to show how White kept focusing on defending the e-Pawn and eventually lost.
Hummm ... that would make sense ... but I didn't get that from the book. Silman Seems to start out discussing the plans both sides should take due to the imbalances ... as quoted here:
White’s extra central space, given to him by the e5 pawn, won’t prove very useful because he will be too busy defending e5. That leaves us contemplating White’s lead in development (will it give him an initiative?). In the present situation, Black will be able to castle quickly and the absence of any weakness will make it impossible for White to profit from his temporary plus.
The goals of both sides should now be clear: White must defend his e5-pawn and find a way to advance his Knights to make them active. Black will play to keep the enemy Knights at bay ... etc
Not following ... the my quote from the book (above) was from him himself ... Silman was outlining the analysis of the existing imbalances in his first example - as a way of giving an initial definition of imbalances ...
then he was developing a correct plan for both white and black (the quote) ... this comes before any of the example amateur's games ... I'm already through that first chapter ... I'm about 1/2 through the book.
He discussed this position of this game in chapter one, and he makes this point:
"The goals of both sides should now be clear: White must defend his e5-pawn and find a way to advance his Knights and make them active. Black will play to keep the enemy Knights at bay (Steinitz said that the way to beat Knights is to take away all their advanced support points) and to tie White's pieces down to defense of e5."
I don't understand the importance of e5. Why is it so important that it would be the overriding concern of both players?