This is the reason I think it is so difficult to judge how well CM:SF has done. If you look only at MP stats (clubs/ladders, even the BFC forums) its clear that CM:SF relative to CMx1 does not have a strong community based around it. However, not only does asymmetrical warfare present a subpar basis for competitive play, but the 2? year period of relative unplayability (especially PBEMs) sucked out any inertia CM:SF had of forming a large online community. Furthermore, its not like CM games are the pinnacle of online access and ease of use. PBEM is a relatively rare style of play outside of dedicated wargaming communities, and direct connect RT play creates a barrier to any type of quick and easy online play.The biggest single problem was that CMSF was a piece of crap when it was released--and for a very long time thereafter.
Its frankly impossible to judge how well CM:SF is doing outside of online wargame players. I would imagine, those players are mostly made up of those who went online with CMx1 and how many CMx1 players went online relative to total sales. Only Steve has access to those numbers and we will probably never know.
Also I dislike bringing it up in this way, but how many sales did BFC make on CM:SF's initial sales. It is quite possible that CM:SF outsold CM:BO drawing in the CMx1 crowd and new players. These people would have all bought it at full price, and even if only 30%(or less!) of them stayed with the game its quite possible that BFC made a killing on initial sales.