The Wikipedia article mentions other applications than notepad and implies IsTextUnicode was fixed in Vista.
Kaplan's blog post explains the change in Vista was actually in notepad (use a different algorithm) and IsTextUnicode was left broken, so the other applications mentioned in the Wiki page would presumably still be broken on Vista and above.
Edit: I was looking at one of the sources of the Wikipedia article and mistook the tab for that post. My bad.