Good writing most certainly is, as I said, "part" of Ben's success as is the you-are-there storytelling. You know, stream of consciousness. The thing a few others have done, including Proust -- for 3,000 pages.
The other part of his success? Good question. I'd have to defer here since, for the life of me, I can't figure out why TPG and MMS (for example) are successful and they're both so poorly written as to be border-line unreadable. I can't figure it out, in other words.
As as for Littewinglet's earlier comment, he did not "nail it." His comment is, in fact, absurd: Ben is a (very, very minor) celebrity precisely because his blog caught on. It's not the other way around. His blog was successful before anyone had heard of him and while he was still an early twenty-something just out of school . . . and still in school. His blog isn't successful "because" he's a minor celebrity. Saying so gets it exactly backwards.
Full disclosure: I skip most of the credit card posts; I can't stand the whole gay camp thing; and I have zero interest in music for 13-year-old girls.