If you count iOMG it's a five-part Seddie story line if it was resolved in just one episode like iSYL it wouldn't show the growth in their relationship. It's a little change in not the dynamic of Sam and Freddie, but the whole iCarly trio. I think this five-part arc (again if count iOMG) was need because it shows how Sam, Freddie and Carly have grown. In my opinion, Sam and Freddie as individuals have changed and their relationship has changed the most. The only thing that bugs me is when they shot episodes without Carly it's iCarly not iSeddie.