Many people really struggle to type on a keyboard - it's something that geeks often forget (I've been reminded of this again this week when helping my mum setup her new laptop). For them, having to enter their email address twice isn't suboptimal - it's a nightmare.

Those of us who don't have a problem with keyboards don't bother typing twice. We Ctrl-A, Ctrl-C, Tab, Ctrl-V, which renders the whole thing pointless.