Yes, styles are data sent and stored in same way as midifiles, but
maybe most people talk about midifiles as recorded songs ready for
playback?
Technics and Ketron have a feature called "pianist-mode" who let you
play with the styles even if you play as a pianist. Besides of that,
it's also possible to play manual bass, so the use of styles sure
can be varied a lot.
Repetitions? Well, as far as I can hear, most all songs are build up
by a lot of repeats. Intro, verse, refrain, bridge and end.
But then again, good keyboards and well made styles don't have to be
boring, even my old KN1000 had a nice feature called "dynamic accomp"
who made some nice changes simply by press the left hand keys a bit
harder.

Happy Playing
GJ