It also wasn't just TechCrunch who had articles about Mailbox. The Verge had 4 articles in less than a month.
Pretty much every tech news website had quite a few articles about Mailbox, as well as major blogs like Daring Fireball which have a huge readership of iPhone users.
It seems weird to me that this blog post attributes the entire success of Mailbox to TechCrunch, when really, Mailbox's success is because they created a simple and enjoyable email app.