I would check that information out. That 97% sound really high. Doing a quick search on google reveals other surveys with IE vs Netscape. Netscape is about 15% to IE's like 65-70%. (The rest of them use Lynx like me.. he he he). Anyway your question is more of a client side ethical question than a PHP.
IE is in the lead by far right now (man you would think this browser gets shipped with an operating system or something to be this popular :-J ), however would you really like to leave out a potential 20% of your customers? To your comment about netscape doing "anti-IE" things try the reverse of that. Netscape was the first to release a browser before IE. Netscape came up with Javascript, then IE (surprise surprise) came out with a language called JScript. Which although similar had some differences, therefore whenever you right Javascript/JScript, you have to make sure it works in both.
Netscape has it problems, but they are getting better. I personally use Galeon (Mozilla engine) and it runs fine on almost all sites.
So this is all to say, for right now, until browser ppl adhear to some hard standards (W3C is a start) I at least will design site to support both IE and Netscape engines.
My 2 1/2 cents.