[pyrmont]

This is a terrible article.

The bald assertion that Tumblr is more successful than Posterous because it is faster is repeated about a half dozen times during the piece but no evidence is ever advanced to prove this point.

Without further data, at best, we're talking a correlation. I could similarly argue that dropping the 'e' in Tumblr is a 'big reason' Tumblr is more successful than Posterous (which, please note, contains an 'e'!).

[coachwei]

Does a fast site help improve business success(comparing to a slower site similar in functionality)? Of course it does. Does performance play a role? It does. Is it the only reason? No.

The article does not pinpoint the success or failure of a business into a single reason. The article didn't claim "performance is The reason" that Tumblr is successful. It says "performance is most likely one of the key factors".