In a blog article posted recently, I pointed out that the SMTP service had been removed from Vista. In an article in one of the IIS Team blogs, Bill explains this as follows: "The SMTP server has always fit under the 'IIS' umbrella, but wasn't actually owned by the IIS team. The folks that owned it have decided to no longer ship it in Vista (the Windows client SKU) and instead are only shipping it in Longhorn Server."
So a team decided just to not ship it. Nice to know that this was a conscious decision. Sadly, it's yet another regression from XP, and one more reason to stick with XP on my laptop. For me, and others, a better answer would have been for IIS to take ownership of the SMTP service.