[martin]

You might be surprised. Keep in mind that developing for IE6 isn't necessarily difficult if you don't care about standards compliance or cross-browser compatibility. In a corporate environment where IT is a cost center, it's often acceptable to support only a single browser company-wide if it means saving money.

Also, a lot of corporate IT shops are not doing anything particularly interesting technology-wise, and have already built IE6-compatible frameworks that make most of the front-end web development they need to do easy enough. On the other hand, upgrading to IE7 would mean exhaustive testing of all existing applications, and the support of "the business" to expend resources on the project. It's much easier to do nothing for as long as possible.

Just to add another data point - I work for a SaaS company serving the financial industry, and 25% of our user base is still on IE6. (We still have major clients running Windows 2000 too, but that's another story.)