Should employer expect full commitment from a temporary, contracted employee?

yes they should specially from proffisionals, thus the contracted employee must show loyality and full commitment as well

typically contractual employees are taken when an organisation does not want to invest in people or they need a skill for a limited period or just a replacement for a short period...
This means the person contracted knows the relationship is not long term , so chances are that during the contract they have eyes open for better opportunities and roles which would be more full filling so at times they are not very committed they are just restricted to their duties alone.
At time you do have people who prefer contract mode of employment..
At times it makes sense and weigh your needs for contract..
if its a critical requirement always have them on your rolls as you have more control