Why does a Microsoft wheel mouse require software installation?

I've found that both Microsoft's and Logitech's mouse support software
is either lacking, or causes problems with other applications, or both.
I would advise avoiding such software unless you *absolutely* have to.

I run Logitech Mouseware v9.60 to get the two middle buttons on my
trackball, but my Logitech MX700 (USB, wireless) is perfectly
satisfactory without the software (which breaks Mozilla application
support for the middle button).

I've had similar issues with the Intellipoint software, I occasionally
use the MS trackball for my laptop, so I do without the software now.