I don't get your comment. Web based email. All I have ever used in my life.
Tablet without email is reasonable IMO.
On the Xoom, it notifies me if anything happens and my email is a home screen widget - the process seems significantly smoother and faster this way.
If I were to have a tablet I think I'd only use it at home, among family members and enjoying my free time. In that case NO email is that important to require immediate action, and for the few, inevitable exceptions (web-server going down, payment system not working etc.) I've instructed my boss to call me on the phone directly.
But that's as far as it goes. I'm not a manager. When I'm at work on my computer, I want my email client to not pester me. Instead, I will go to it once or twice a day when I've reached a natural pause in my work. When I'm at home on my tablet, I want my email client to not pester me. Instead, I want to read the news, watch a movie, or otherwise enjoy myself unmolested. If something is urgent, I can receive calls and pages on my phone. My phone has an email client. I don't want it to pester me, either.