I'm a purist when it comes to using milks/creams, et al. IMHO, it's not a 'milk soap', if there is other than milk used as liquid. The fresher, the better.
I'd really like to see soaps that use milk as an additive (i.e. part of the liquid) be identified as such. But that's just me ... not everyone can have a goat or cow in their back yard and get fresh milk!
eta: the heat of pastuerization also kills all the wonderful benefits of milk ... the use of dry milk have even less benefits. But of course both are enriched and fortified with other additives!