It's an unfortunate example of tribalism (cue very appropriate Life of Brian quotes...). Sadly, there are Ancients/medieval players who haven't seen the light of DBMM!
Some of them seem to have become soured by the development process, some of them have at least made the effort of reading and playing the finished version before condemning it. I feel that a lot have been put off simply because their clique says DBMM's got rules holes etc in it - of which there are occasional examples but not as many or as serious as rumour would have it. Some of teh tournament players took umbrage about some of Phil's comments about tournament players during the development process. Seems an odd thing to let get in your way of having a good gaming experience, but there you go.
It's their loss, of course, but it does diminish our enjoyment too.
The 3-way split of DBM into FoG, DBMM and 3.1 players is very sad. There are certainly guys playing both (Dave Ruddock is a FoG-ite who seems to play a fair bit of DBMM, Richard Jeffrey-Cook is playing both games in 25mm scale, to quote two examples). However, for myself the reason why I haven't yet played FoG (despite owning the rules and all the published supplements) is that I just haven't had the me-time to do both. I wouldn't be surprised if that weren't the most common reason of all.
Here is the UK I also get the impression that there's a bit of an entrenchment thing going on. DBMers are happy with DBM and are don't see why they should abandon a game they still enjoy. Some of them don't want DBMM to succeed, as they're still hoping that we'll come back into the non-FoG fold. FoG-ers have "taken the plunge" away from the Barker rules, and don't want to go back at the moment. DBMMers are being proudly non-conformist...
Tim Child