WMVs are not 29.97 fps? Why do they round up?

[Hareoic]

I find this really really really weird. While the DV-AVI of WMM saves movies at the usual 29.97 frames per second, VirtualDubMod tells me that the highest quality WMV save available (video for local playback(2.1 mbps)) goes at exactly 30 frames per second. Hard to say how much of a difference it makes, but I never saw anything posted about this and wondered if I should save footage at 30 fps instead of 29.97 (since DV-AVI refuses to work for me) or just ignore it.