Like an old married couple

[queenoftheDales]

As you know, it's very easy to start believing in alternate realities.

Who knows what Sheldon and Penny could have been if the writers had decided to to go that route. Pilot Fish is right though, Sheldon and Penny used to spend a lot of time together and they still are always touching each other (despite Sheldon's mysophobia). It seems like it's the only relationship tptb are able to write successfully.