>> I was told at a graduate visit day at UMD that they don't accept credit from MS programs other than their own
I don't know how common this is.
I know lots of people (probably most) that get their Master's at a different place than their BS, but don't know any that got a PhD at a different place than their Master's - maybe because as you say the barriers to moving are too high. People that aren't happy where they got their Master's don't get a PhD at all.
I know lots of people (probably most) that get their Master's at a different place than their BS, but don't know any that got a PhD at a different place than their Master's - maybe because as you say the barriers to moving are too high. People that aren't happy where they got their Master's don't get a PhD at all.
(My experience is with the U.S. system)