It only has the updated rsa key pre-inserted, the v21, v22 and v23 have an update function to update the key manually (it's all mentioned in the OP).
Excuse the n00b question, but what's the exact difference between TechBench and MSDN ISOs? Aren't they both the same as retail versions?
They're the same. I just downloaded the ISO from Microsoft's page and verified the checksum is the same as the one on MSDN. P.S. Thank god, finally the pt-pt Pro x64 ISO is here!