RP's, when good (and even sometimes when not), tend to do that. Personally, I think Hojo's title was implied in order to give him an 'educated' status in the player's mind. Dr. would have done the same thing, but that would have implied medical practice; while his research was similar, it was not the same. It would be interesting to see what his title was in the Japanese versions. Was is Hojo-san, or sempai, or something else altogether?

Hee. Snape + Hojo = Scarred For Life.