Wow, I didn't know that. Also, only 75 USD per virtual server. For some reason I had a much higher number in my head. Happy to pay this (and support the Ubuntu team) to keep some old boxes up for a couple more years.
If you have a cluster of virtualization hosts, you can license each physical server for 225 a year. It will then cover all vms on that physical host. I went over this multiple times with Canonical reps before purchasing as it seemed too good to be true, but it is. It doesn't even matter what hypervisor you are using.