Why Does LAUNCH.com Use WMV 8 instead of WMV 9?

I have downloaded a few music videos from LAUNCH.com recently and I was curious how they encoded their videos. The interesting thing I found is they use WMA 9 but they use WMV 8 instead of 9 even with the newest videos on the site. Is there better compatability with WMV 8 than with 9? I thought that there was backward compatability with the WMV and WMA codecs. Can anyone answer this?