Actually, it is a good question. I think it is important to note how the process works here. The patent pool administered by MPEG-LA only includes issued patents. And it is up to each company to provide their patents to be evaluated against the standard as otherwise, they won't be included in the list, even if they read on the spec. So this is not the case of us showing them 100 patents, and them "awarding" two of them.
Microsoft currently has many patents for VC-1 technology under application status, as it takes five years or more for patents to be granted. Therefore, we expect Microsoft's patent position with respect to VC-1 to increase significantly over the next few years. More important than the sheer number of patents, however, is the level of innovation reflected in those patents. Many of the patents in the current list refer to older codec algorithms, whereas Microsoft's patents and pending patent applications reflect the core innovations in the codec.
The same is true of other pools btw. Some 150 companies contributed to AVC for example but I believe only 25 are represented in MPEG-LA pool today. As the new entrants have their patents granted and they choose to participate in AVC pool, the list will grow and percentage of patents from each company will change.