It's secured against assets that may not be worth tomorrow what they are today. Imagine if you stopped paying your mortgage, and the bank sells your house, but they only make 5% of what you paid for it because the price of houses in ubercow's neighbourhood happened to plummet recently. Now somebody else has your house, but you still owe the bank almost all the money.
But the assets are always sold before you are allowed to use the funds from those sales on RH. I don't think that analogy works. In the end, if your assets plummet in value, you don't owe RH all the money because you have already paid them it, through a bank transfer or stock stale which is already completed at a known price before you could spend those funds.
It's like a mortgage with a 100% deposit. You might technically owe money at some point, but you have already covered it completely. And the bank isn't going to sell your house because they know the full value of the mortgage in cash is already on the way to them.
