" for a (highly negotiable) fee"
Oh, now I see. As you were.
While Postgresql does use the Apache model, there is middleware available (google 'pgpool' for an example) that amongst other things will queue requests so they can be serviced by a limited number of children. Of course this only matters if there are an awful lot of simultaneous queries (without the corresponding amount of server RAM).
However; your claim about threads per CPU is oversimplified, and especially wrong with a DB server where processes will most likely be IO bound. With 1 core, for example, there is nothing wrong with having 5 processes parsing and planning a query for a few microseconds, while the 6th is monopolising IO actually retrieving query results. Or the reverse - having 1 CPU-bound process occasionally being interrupted to service 5 IO bound processes, which would negligibly impact the CPU-bound query, while hugely improving latency on the IO bound queries.