Rather then using different CSS files for different browsers you can also achieve the same results using a single CSS file. If you keep your style strict by defining every attribute of the tag, specially i encourage redefining every tag to your own as mostly different browsers render them differently, let say Paragraph tag normally add margin and padding to top and bottom, which is rendered differently in different browsers.
At WebComers we try to provide similar services, keeping my code simple to a single CSS file, don’t add extra code specially JS as due to security reasons firewalls tend to block it. I disagree with the concept of using extra CSS files.
90% of the people are not computer techie. There are few people who don’t even know anything except clicking on IE icons as it comes pre-installed with Windows. The second reason might be that we Web Developers/Designers mostly work on e-commerce or business promoting sites for general public, and they are geographically dispersed around all the world may be there is someone who is also accessing internet from Mars.
This post is written in response to http://www.smashingmagazine.com/2009/12/01/how-to-support-internet-explorer-and-still-be-cutting-edge/comment-page-1/#comment-421052 on Smashing Magazine.