Some more info: http://en.wikipedia.org/wiki/Fractional_ownership
You own a fraction of the land that the building sits on, and a fraction of the "common areas" (lobby, swimming pool, parking lot, etc). You are responsible for contributing for the maintenance of those areas, or paying assessment fees to a management company that will take care of those areas.
Like, if the ground rental brings in $10,000 per year to the owner of the title, and I came along and said, "I will pay your $1,000,000 for the title," well... I'm offering you one century's worth of ground-use fees up-front. Presumably all but the most irrational actors would sell their ground.
I mean, the same guy ("Tom") is going to be giving you money one way or the other. Either in bits and pieces as ground lease, or in lump-sum as purchase.
If you simply want more money than Tom can pay, well, you're out of luck. You don't get any money if you price your tenants out of the market.
If there is an amount of money that Tom can afford to pay in ground leases, then why can't he get a bank loan and make you an attractive offer on the purchase? My earlier example of 100 years rent was extreme to make a point. What if Tom offered you 20 years land rent in an up-front lump sum? Maybe not every land-owner would consider that a good deal, but it's hard to imagine that none of them would. The land-owner gets a present value that exceeds the future value of the rent to them, the bank gets interest, Tom gets synergistic value from now owning not just the house but the land.
The intention is to keep house prices affordable. (Sort of an upscale trailer park, now that I think about it). If you had the means to buy elsewhere, you probably would.
Mortgage providers won't give you a mortgage term that ends after the lease does.
Also, in China, the people (gov) owns the land. We are only entitled to a 70 year lease on it. Oddly enough, this is applied to housing (apartments) also. But China also lacks a property tax and so has all the bad speculation behavior and rent-seeking that goes along with that.