If they haven't upgraded to something better yet and it's FREE to replace and has been for years, what are the odds that they will pay for your service.
Seeing as the majority of IE6 users are in the enterprise market... I'd say the odds are pretty good.
What is the cost of serving them a plain jane experience, as you do with a printer or feed reader? If you can model your audience and quantify the impact (in other words, prove your theory) for your audience, why BLOCK THEM? Just give them the content, minus the design. Spend the same amount of time you spend on your print.css file.
Anything more restrictive than that is not about income, as you suggest - it's about dogma.
Thats what we thought at first too, (as a b2b startup) - except that if they as a company haven't moved on past IE6 they are not very likely to adopt new technology in general - including the startups products.
I wouldn't push for banning IE6 if you are selling a non-tech product, but if you are a tech company and have a feature IE6 holds you back from implementing or are losing time to supporting it, dump it.
Seeing as the majority of IE6 users are in the enterprise market... I'd say the odds are pretty good.