Speaking from a Web/Healthcare IT startup experience: The BIGGEST challenge is that your buyer, user and payer are 3 different entities. Every budding healthcare entrepreneur wants to "disrupt" this somehow, but eventually almost everyone gives up and they either die or become yet-another-enterprisey software company that everyone loves to hate.
You can make a decent, linearly growing business if you can survive 2-3 years long sales cycles. So it makes sense that VC's don't want to venture into this space.
You can make a decent, linearly growing business if you can survive 2-3 years long sales cycles. So it makes sense that VC's don't want to venture into this space.