Well, you can get Virtual PC 7.0 (XP on a virtual machine) for a few hundred dollars, and that would run your critical windows apps on the Mac. The only one I would wonder about would be WS-FTP and SnagIT, but there are many FTP clients and screen capture packages available for Mac that are easy to learn and use.

Many of the software packagaes you mentioned come with the Mac version on the same disk, so you can save money that way, too.

The underlying operating system for OS X is BSD, so you can get most of the applications you find for Linux for BSD, too.

As for positive reasons to buy, you can always use it as a Mac testing machine.