"html is html - unless they are scripted to reject IE I don't see the problem."
There are tons of differences between standard HTML and the extensions Netscape and Microsoft have added to their browsers. Netscape also is the most poorly implemented browser in that it is not compeltely standard.
non-Mozilla Netscape has also been formally dead for several years now. It doesn't even have .5% of the browser market under its control.
I personally don't know anyone that uses anything less than Firefox 1.0, IE 6.0 or Opera 7.0. Nerd and non-nerd, I don't know anyone that uses an old browser anymore.
I have been using Opera 8.0 since it was released and love it. It's quite standards compliant and better IMO than Firefox, especially if you're a Mac user. Any Mac user should switch immediately from Firefox to Opera because it's almost as fast as Safari, but as capable as Firefox.