If I thought that producing commercial software would get me more sales and be easier to write on RISC OS than on another platform I'd write commercial software for RISC OS. Unfortunately reality doesn't seem bear that out.
Many of RISC OS's most talented developers, producers, software houses and even some the dealers branched out into other platforms, not because they disliked RISC OS, but because of the opportunity those other platforms provided them.
I think the days of seeing large commercial applications, something the size of Ovation or Artworks, being written from scratch for RISC OS is far far behind us.
If you won the lottery tomorrow, would you plow all of it into developing RISC OS, or would you realise that the chances of seeing that money again would be incredibly slim?
What's left? porting application from other platforms, updates to existing software, small commercial software and utilities, and continuing to rely on the generous time donated by open source and freeware developers.