Well, I think they must eat just like the rest of us but the tool may stay in same niche of tools like Milkshape, Fragmotion or Ultimateunwrap ; after all those years in the market, with frequent updates I think that those programs do sell well, surely they don't try to compete in the price range of XSI, Cinema 4 or similar softwares.
If 3dBrush can deliver a solid scultping and detail performance at reasonable price, it will become a "must have" application.