ORIGINAL: da Rock
I would think that every developer would have included the capability in their original release.
Well, it could have something to do with this:
ORIGINAL: MSelig
ps I will add that working out the automatic physics behind this is *not* easy.
I.e. it's a non-trivial and non-essential feature, so I'm not sure why you think every sim would include it in its first release. I do agree it would be nice to have though.