Just curious - what's the appeal of non-web-based email? I'm forced to use Outlook at work, but I can't imagine having to install something to get my personal mail, and having to back up my personal mail. Do people do this mostly because they're concerned about their data privacy, or because it's easier to work when you don't have internet access, or what?
You having the full control over your data. Do you really not backup your mails? Do you consider them not important or do you glorify your provider? I highly recommend making your own backups for anything you consider worth saving.
It's the practical realization that Google is likely to have a more recent, redundant backup of my data than me. The amount of effort to ensure that P(losing my backup) < P(google losing a backup) isn't worth the effort except for a few very important pieces of data.