the reason rpm is recommended is simple: everybody is using it. it has become the standard, no matter what LSB or other say.
Well that’s a pretty dumb reason, IMHO. The problem with choosing .rpm over .deb, is that everything that .rpm can do, .deb can also do, but not vice versa. So if they choose .rpm, there will be features that are lost in Debian. Where as if they choose .deb, RedHat can still do everything that they currently do, and they don’ thave to create a nice consistant set of packages, but they can if they want to. RedHat would only lose time in having to convert everything from .rpm to .deb. Debian would lose functionality in having to convert everything from .deb to .rpm.