IE6 wasn't the problem. It was the specs and programmers
Let me start off by saying we have had zero issues with building modern applications that handle older browsers. We have a couple released in the past year that work in everything released since IE5.5... and they take advantage of later standards when the browser supports them.
However, what I've seen happen with other development companies is that they'll bid on a project. The sponsor will say, it MUST work in IE6. The dev company then says Not a problem. Then promptly takes advantage of all the broken crap in IE6 that isn't supported by anything else. Project is delivered and sponsor pays for it.
So, who's to blame here? I say it's the development company. They could have made it work in not just IE6, but others as well. Without a single issue. However, most web developers quite frankly don't know what they are doing. They use point and click tools and little code snippets they find out on the web.
How does this get fixed? First off, it has nothing to do with the price of the project and EVERYTHING to do with the quality of the people building the software. I'd like to say only use developers or companies in a particular country or price range... But even that isn't accurate.
The only real answer is that the people in charge of buying the software need to be smarter. They need to know how to really evaluate bids and the quality of the bidders. Good luck with that.