Actually I think the way DMC was handled since 4 by the developers and the press fuelled this division as well.
It doesn't help that developer maintains silence on some things, and introduces wild changes and new characters in 4 without cue or explanation. That divided the fanbase at that point too. I remember the polarized attitudes when Nero came into existence and how passionate some people just were about it. Maybe the DMC fanbase in general is a small but passionate one.
It doesn't help that the 'controversy' generated by saying the old DMC Dante was uncool (and by association if you liked old Dante you could be labelled also, this probably by some fans took it personally) was ridden like a wave instead of being defused by the developers. On official boards people who criticised the new incarnation early on (and sometimes in only MILD ways) were silenced, and later 'haters' were actually blamed for poor sales by lame journalists.
This whole thing was like a fire people kept putting fuel to, and I wouldn't be surprised if it was done just to raise visibility and keep this thing a hot topic for 2 years.
Otherwise, it's just people being anal, or they have defective personalities or something. I've got an opinion on DMC and DmC, but I'm not an ass about it, unlike some people.