I certainly wouldn't have thought twice about the very small difference in speed on my system.
It's possible all the Photoshop engineers have very powerful systems - it would make sense.
Beta testers tend to be well-outfitted as well, so they might not have seen it.
We don't know what kind of system testing the product goes through on what kinds of machines, but I imagine it's substantial. However, it's possible that if a step generates a valid result an automated test suite might not notice it took 10x longer than its predecessor.
No, it's not hard to imagine how this slipped out.
-Noel