I think the reason this feature is in i-movie and not in FCP is that higher level software does not try to figure out what the user actually intended. That is because most experienced user know what they want, and object to the software acting inconsistently.
For example, a video may be nearly finished and timed for a particular length, but then a transition is added of two seconds somewhere in the middle. If there are handles available, the piece would stay the same length. If there were no handles available, then the completed piece would be 1 second shorter, as the editing program forces a shortening to handle the transition.
I think that precise timeline positioning should takes precedence over adjustments for improperly formed transitions.