There are many ways of supporting equipment, and (as I have said a few times before), in theory
it doesn't matter how kit gets maintained just as long as it does
(that is, everything is covered). But surely by now we all agree that there is more to in-house biomedical engineering than just repairing the kit once it breaks down (like getting off your idle butt and walking around the user departments, rather than sitting there reading a book, for instance)!
And anyway, that last "model" you mentioned is undoubtedly the worst of all the options. There are many reasons, but here are just three:-
1) Nurses et al
don't get the direct support they need
2) Fixed equipment cannot be sent off (so will still need to be visited)
3) The dispatcher becomes a tyrant!