Linux was able to grow and prosper due to the fact that the code was portable and therefor Linux was able to run it.
If Sun had managed to get people programming just for it (the way that people are advocating programming only for Linux) back in the days when it was the premier OS, Linux would have been much harder to get started.
Linux developers today owe it to everyone (including themselves) to not raise the bar for for the eventual linux replacement higher unnecessarily.
that being said, having software take advantage of the latest features is a good thing, but the software should degrade gracefully in the absence of those latest features. This may mean falling back to something not as good, or it may mean disabling some features where there is no fallback.