Hey Peter,
An O/S actually isn't there to run apps. An O/S is there for Apps to use. An important distinction when saying that WinXP is great because it runs the Garmin Trainer, and Win7 is rubbish because it doesn't!
As SoCal correctly indicated - it's the app's fault, not the O/S.
Would you say that non-certified aircraft are better, because they can run non-standardised avionics? If the avionics are not certified for your aircraft does that make your aircraft at fault or the avionics (by way of it not being certified - like software not being written correctly to correct standards)?
I think it sounds like a fair statement from you would be "For my personal purposes, WinXP seems to be better", but a blanket "WinXP is the best OS and there is no point to Vista / Win7" is what I was suggesting was very misguided.
My company has systems running pretty much every current operating system there is, from Linux, to MacOS, to Win7 and a whole host of stuff in between, including one or two simple operating systems we've built from scratch. These are installed on everything from embedded devices, to laptops, to tablets, to pcs, to clustered servers, etc, etc. And being run around the world, sometimes in a data center in London, and sometimes on the side of an Argentinian mountain, or a minus 30 degree Swedish forest. We set up huge WAN networks in remote locations, with no local power or comms, within 2 days, and we've been doing this for over 10 years - originally using WinXP.
I can give you a cast iron guarantee, that your personal opinion of WinXP vs Win 7 is false - except in extremely isolated cases, yours (aparently) being one of them. It's all academic anyway. If WinXP does what you need and you're happy with it, go for your life. I think it was just the (even you must admit) overly opinionated statement that your obsolete OS that you happen to use is "the best" and everyone has just got it wrong.