I think the problem with this model is a question of scaling. Suppose I write a fitting program which I sell. Sure, I have to support it for some fraction of users, but for the most part, I have the initial cost of creating/marketing it, but everything above that is profits. If I am selling support, I have to have enough people to cover the support and naively, I think that the costs scale with the number of sales (and one support engineer can only cover so many customers)--so, the only way I can win is if I charge a lot for service.....