Dave,
 
I've seen deer eat a variety of plants - some because they like them and some because they're forced to eat them (because there's little/nothing else to eat). 

Preference trials can be somewhat skewed by the choice of plants available to deer. 

For example, if you performed a preference trial of 5 species (striped maple, rhododendron, mountain laurel, New York fern, and hornbeam), guess what - striped maple would be listed as most preferred. 

This is an exaggerated example but it demonstrates the possibilities in preference trials. 

Kip P. Adams
Wildlife Biologist
QDMA