The number of desktop-based products closed by Google is far more significant, as a percent of those released. Basically, excluding obviously Chrome, they are shutting down every single desktop tool (toolbars, plugins, desktop search, enterprise syncing tools, etc.).
I don't think it's unreasonable to forecast that this IE9 plugin might get discontinued at some point for a combination of { no traction, better alternatives from ffmpeg/vlc, irrelevance of VP8 when VP9 is out }. At the same time, I can't see it as a crucial part of any business (I doubt there will be any WebM-based business soon, for now), so I don't see a real problem in getting/using it while it exists.
To add to the list of reasonable reasons for discontinuing products, there's also the question of relevance. If WebM support is added to some future IE version (not out of the question if WebRTC in its current form catches on), will the WebM plugin get added to that list? That's exactly what happened with things like Google Desktop, which I used to love but became completely superfluous when windows added a decent file search. Not everything needs to last forever, especially for desktop utilities and libraries, where the most useful tend to be folded into the OS itself over time (see: "sherlocked").
I don't think it's unreasonable to forecast that this IE9 plugin might get discontinued at some point for a combination of { no traction, better alternatives from ffmpeg/vlc, irrelevance of VP8 when VP9 is out }. At the same time, I can't see it as a crucial part of any business (I doubt there will be any WebM-based business soon, for now), so I don't see a real problem in getting/using it while it exists.