Did you ever notice that whenever Family Matters would show an episode dealing with a serious topic, that he wasn't really seen in it that much? Like in the episode when Harriet and Rachel's father returns after years of not seeing them. Or in the one when Laura wants a Black History Class in School and gets Racially insulted. I guess since the charachter of Urkel was far from Serious, the writers figured it was best to keep him in the background in episodes like that. What does everybody else think?

That's probably true. But there would seem to be exceptions. Steve played a significant role in the gun episode, speaking up against guns at many stages of the episode.

Yeah there was another serious episode in which Steve was just a background. The one where Eddie and Carl fight because Eddie lost the screw driver and got grounded and then he snuck out and Harriette mediates their feud.

Or sometimes if they had serious episodes they would give Steve a subplot. Like the episode when Carl felt guilty about the hostage being killed and he was not able to save him. Steve's subplot involved trying to get Laura to go to a Johnny Gill concert. And another one was in season 5, I believe when Eddie got pulled over by the cops, Urkel had the wacky subplot involving taking Richie to the dentist and ended up causing havoc.
Another serious episode in which Urkel had a main role also was when he helped his classmate who had Leukemia.

What about that eps where Steve accidently takes Laura's diet pills.