The interesting figure here isn't the 6/10. It's the 4/10. I'd have to question the sanity of that 40%. This is not a bash at MS. It is just prudent IT policy, and good business not to use untested software in mission critical environments. No new OS, from anyone, is guaranteed to be mission critical in its first year of release.
Most of those 4/10 already have their hands on the OS and are testing it. Many large corporations are given prerelease versions for application testing prior to the street release date. If any of them were going live on day 1 with no testing that would be insane, but i bet most will have been testing extensively prior to october.