FWIW: At my office, we changed over to 64 bit a few years ago. The number of support calls we had before the change from customers who were having issues due to the 32 bit version not having enough resource capability was at least an order of magnitude higher than the calls after the change of users who still wanted 32 bit support. Every last one of them upgraded to a 64 bit OS once they understood why we made the change. There is no way of knowing if we lost some users on the transition as it is possible they just dropped our product and never contacted us about it.

In our case, nearly all users were feeling some pain due to the 32 bit limits. Since this was a pre-existing product, we did a fairly extensive awareness campaign starting about a year earlier that we were going fully to 64 bit.

We had considered doing both 32 and 64 bit versions, but a bit of market research with our existing customers showed that much less than 1% of them wanted us to continue supporting the 32 bit product. They preferred that we utilize our time solely on the 64 bit platform.