Again, remember that “many parametric cad” are all using the same geometric kernel and thus have access to the same type of operations. There are only a few common kernels. (@bob, this page is actually incorrect concerning Rhino) ACIS and Parasolid account for most of the most popular MCAD software packages…
With something like ACIS or Parasolid, you have dozens of high-priced software leasing the same kernel which makes for a lot of money coming in to the kernel developers to pay for further development. And they only have to develop the geometry part, not the interface or anything else.
There’s no way Rhino can compete with that, money from sales has to go to the development of the entire program, not just its own “home-grown” geometric kernel; and there are no economies of scale to be had by developing that kernel for others and deriving additional income from licensing.
That’s just how life is in the fast lane, Rhino still offers many, many things the other packages don’t, and does a lot of things better than other software, but solid modeling with fillets and shelling just isn’t one of them.
–Mitch