Yea, it's one of my 2 major pet peeves with GMRS and the two are linked by those who claim to understand but don't really know any more than the rest of us.
There are some differences in equipment. Handhelds are even defined by equipment, and per FCC as Steve also suggested, handheld is a sub-type of mobile where regulations don't specify separate rules, Base stations have an antenna in a fixed position. Mobile is normally straight forward but can get a little fuzzy in some circumstances.
To me, their clarification indicates it's the linking itself that is not intended, not just use of phone or internet. Linking by any technology has a lot of the same drawbacks (tying up channels, potential for interference, etc.). It's not just PSTN or internet but the linking itself that is a concern. True that they didn't update the regs, but interpretation by FCC is a lot better IMO than interpretation by Billy Joe and Bobby on the internet. For those who want to challenge it because the clarification wasn't incorporated into the wording in the regs, y'all go ahead and see what happens.