Joe --
What I think this indicates is that all the vendors are moving up-market, and up-market customers wants the features available from Unity 3D -- namely, the web-based viewer.
This is the same way that a lot of corporate websites use Flash. It offers stuff that regular HTML websites don't -- but requires professional, expensive development.
OpenSim is a low-cost option -- and, as a result, a low-revenue option for vendors, unless they're working in bulk.
But as established vendors are moving upstream, I expect to see even more vendors showing on the low end, offering OpenSim hosting, support, and development services. Dreamland Metaverse is going well, and SouthPaw Estates just joined up, and Kitely keeps adding more and more land area, and the number of public grids we track just passed 200.
It's the circle of life. :-)