I think the writers had him say that so that they could subtly make a point while still being funny. What this shows is that Penny could get Leonard to do anything she wanted to (not necessarily intentionally), if Leonard thought he'd get sex. This reveals that Leonard was a bit of a push-over, and he needs to get over it for him and Penny to have a successful relationship down the road.
It all goes back to the "take charge Leonard" that Penny said that she liked, as well as Penny saying "You don't always have to go along with the girl wants" in season 2.
Once Leonard learns these lessons (he is getting better at it, but of course he reverted to the old Leonard once Penny paid him a compliment) he and Penny will be much better off.
I think it's obvious they still have feelings for each other. I could sense it in their fight.
Oh and the Sheldon bird scenes were absolutely hilarious lol