You have a good point.
Company I work for has oversight over supported 5million workstations.
We just finished qualifying windows 7sp1 and ie9.
As soon as ie10 rolled in came the calls why doesn't this work in ie10.
Well our answer was its not supported yet. We didn't approve this update and its not in the qualified release notes that were distributed.
Unfortunately with a complete system app that requires dedicated workstations, you can't keep up with the latest and greatest right away.
We skipped windows 8 and are evaluating windows 8.1
If you are making a massive system app, customers shouldn't have expectation it would work on versions/updates not specified as per a contractual obligation.
If you are simply making addons, you should be in constant communication with the vendor so you support X if they are going to support X. Otherwise you gonna lose business...
We have 3rd party vendors that are being dropped in our new release because they don't support it yet.
For the big players we are working with them so we are going live with them
I'm not sure I could complain, but we are a super vendor with all the privileges, we are still about 6-12months behind MS releases at least.
Its all about setting expectations. And you can't officially support something that hasn't been GA'd yet.