You are not the typical user; what makes 37Signals so good is that they clearly understand just how dumb typical users are and design apps normal users can actually use without having to get their tech buddy to explain it to them.

And honestly, it's not dumb enough. Email dominates the workflow of most businesses because that's about the complexity most users can handle, write mail, send button. I've seen people use Basecamp for weeks and still be confused by the fact that there's more than one tab.