Since the site is open to 13 year olds and up, Yahoo made the determination about what content should and should not be allowed. They don't allow cursing. When the site first started, curse words were no blanked out like that. But they could not keep up with removing all the foul language being displayed as a result, so they instituted the use of the asterisks to 'hide' the words. Questions and answers can still be removed for cursing, even if the actual words are starred out, though, as the intent is still there -- which means it is still a violation.
well some younger kids mightnt be able to figure out what the word was. Also if not asteriked out, some people would report the answer as offensive, then yahoo is obliged to remove it altogether, even tho its a good answer and a lot of people arent offended by the swear word. They cant really report it and say theres asteriks but i know its a rude word so pls remove it