I don't like the idea of making someone sit there waiting for their opponent to complete their turn.
But... if it's via email... And someone wants to play a game with a buddy... Then they have to wait even longer for emails to get sent, opened, replied to, etc etc.
I don't see the logic behind not wanting to make people wait, and yet making them wait longer.
There's a game by Matrix Games (can't remember which one) that would have been a great game if it hadn't done something very much like this. Their approach was to upload the turn to a server and the opponent would then download it (or log in later and download it). But since it was unbearably slow to play that way myself and my buddy that forked out cash for it set it on the shelf and haven't looked at it since. And I hate to say it but I won't buy another game like that.
So here's a formal request... Add direct connection network support. :)