I can answer that;
(mainly because I am not in the chain of responsibility)
Because there are too many links in the chain,
and because it is too easily forgotten once a house is sold,
and because it really doesn't matter!
You cannot buy a house through Trulia,
you have to see a Realtor to get the latest information.... more
There are some mobile home parks set up as condominiums. So you'd purchase both the home and the land it sits on. However, keep in mind that you'd still have a condo fee. And it'd probably be comparable to the ground rent you'd pay, since it'd have to cover the same amenities and services in the park. Plus, of course, you'd pay property tax.
But for people who'd just feel more comfortable owning the land, there are some parks out there that you can do that with.