Why do people think family guy copies simpsons?

I am a huge family guy fan and it annoys me when people say family guy copies the simpsons. The classics had some borrowed storylines but since being cancelled for the second time and bought back family guy has been very original and hilarious and yet it is still accused of copying? The characters are very different and saying family guy is copying the simpsons is basically like saying any animated family based show is copying simpsons? Anybody have any other opinions?