Things I consider bosses in DMC4, Credo, Agnus, Saviour, Sanctus, Bael/Dagon, Berial and the Echidna
That's 7 as far as I am concerned, and to be honest Saviour didn't work much like a boss until the last phase, the first phase you are climbing around a level fighting enemies and pushing buttons basically (buttons being attacking the blue things on him).
Yes you do first many of the bosses more than once, which I did find fun, but it's still not 10 bosses.
Also the last boss was considerably easier than the rest of them, which I hate.
Oh yeah, and Dante makes 8, even though some parts of that boss fight were ridiculous (shotgun).