If Chrome, Firefox and Safari didn't collectively give users a better experience than IE, then why would anyone switch from what's pre-installed? They have to be better by definition.
There is two basic reasons people use these aftermarket browsers:
1. Speed - they are faster than IE and as I explained above the reason they are faster is because they contain less code. The tradeoff to this comes with the fact they are also less capable.
2. Anti-Microsoft sentiment. Yes, there is A LOT of this and it comes from IT pros and end users alike. ANY company that achieves mega-success goes through this. Apple is also experiencing it more than ever these days. People get this notion in their head that XYZ company has gotten too big and too arrogant and they look for another solution even if it's not as good. In their head they believe it's better even though it really isn't. For example, from a network standpoint NO ONE comes close to AT&T and Verizon when it comes to cellular phone service but there are millions of people who are using Sprint, Nationwide Cellular, Metro PCS, etc. just because they don't want to be part of the large companies which they preceive as being monopolies. There's some of that going one with Microsoft/IE as well.