1. Our app is very interactive, and we didn't want to have to deal with incompatibilities.
2. Our target market is (primarily) software developers working for small companies. The only people that use IE6 are people who don't know any better or who are forced to do so, and there are few of those in our target market.
We know that we're probably losing some sales due to our lack of IE6 support, but for the reasons stated above, we're going on the assumption that the additional sales wouldn't offset the cost of development and testing.
I think for a consulting company, it depends on the project. If you're writing something for general consumption or enterprisey software shops, it's much more important (unfortunately) to support IE6.