Exactly, basing the assumption that computers are only about data in->do something->data out, is a bit of an old-fashioned way of thinking. These days, the vast majority of computation involves execution loops:

1 - Display something (perhaps put some data out) 2 - Receive input 3 - do something (perhaps combine input with data in) 4 - goto 1

This is true of everything from video games to operating systems.

Dataflow models are simply a subset of the models of computation we deal with these days...they are extraordinarily useful models, but still limited in what they do.