Finally a dab at a real number. I doubt there are 20,000 systems over 20 K in the USA ...
Going back to my 50 major cities example, that would be 400 systems per city. You could well be correct and I would be comfortable using that number. But I would be totally comfortable saying that there would be no more than 1,000 homes in each of those cities that owned a system whose MSRP was $25,000 or greater, for a total of 50,000.
There are a tad over 100,000,000 households in the US and if 50,000 have systems of this type, then .05% of the number of US homes plays in our hobby at this level. Assuming this numbers are correct (even if you triple them, it doesn't change much), this puts a lot of pressure on the manufacturers (what are there, 200 of them in the high end market?) to maintain growth.
As you move to the OB/Mike Lavigne level of system, I would be surprised if there were 5,000 in the US (this does not include the cost of some of the exotic HT rooms [less equipment] we see whose build cost is probably well over $100K).
Interesting hobby we are involved in.