I think the implication is that any languages built into Visual Studio get an automatic stamp of approval from corporate management, which is why we get millions of lines of code written in C# and VB.net and not, say, Boo or IronPython. Thus, F# will have something previous ML dialects do not: mainstream credibility.

Of course, one could make the same argument for J# -- which shipped in Visual Studio but is now being discontinued for lack of popularity.