Hmm. If you really only want to update records if they really have changed, I can think of two things that might help:
(1) A hidden field for each record in the form, that is normally empty but when a field changes, a Javascript onChange handler fires and sets its value to "changed". Then when the form is submitted the receiving script goes through all the records that are sent back, looking for and updating those whose hidden field is "changed".
(2) examine and compare the existing records with those coming back from the form, and update those that show differences.
(2) is expensive in database terms, while (1) assumes the browser has sufficient Javascript support.