Hey,
I fully understand what you mean and I will try to answer the best I can.
When I compose a film I am effectively providing a service, so the music I write will be what the director (or producers) want. I do alot of independent films at present and one thing that happens alot is that the temp track will be 50% Transformers (if I hear the track 'Arrival to earth' one more time ill hit something) and 50% Hanz Zimmer score (more recently The Dark Knight')
So before I even begin I have restrictions on how far I can take my own compositional voice, If you watch my newer videos I talk about how I am harmonizing themes for the neutral situations...which I have a bit more creative freedom over.
On to another aspect of your question(s)...The Audience. When an audience watches a film they have a certain expectation of the music they are going to hear, and if I go to far from this expectation it can be verry jarring...or even worse, in their mind, the music doesnt work to picture.
At the end of the day my music must work with the picture and let the audience know 'what to feel'and 'whats going on' the most effective way is to use styles they are familiar, and already associate with.
I hope that answers your question.

Dan