I'm of quite a few minds about this!
It's not that surprising. FS can't ever have been a money spinner for MS.
In some respects, add-on developers might actually be breathing a sigh of relief. I can't remember any other time when both the current and previous versions of MSFS have been equally popular. It's normally the case that when a new version comes out, almost everyone switches. That's not been the case this time, and a lot of developers are having to produce FSX and FS9 versions of add-ons, with the prospect of an FS11 around the corner. At least now, they know what they've got to deal with and can concentrate and giving us some really good add-ons.
FSX and FS9 (along with X-Plane) are still there. We can still enjoy them, and get more out of them as the cost of hardware comes down and performance increases. In a couple of years, a rig to fly FSX at max detail at 200 FPS will probably be the norm.
So, it's not all bad news for simmers. Nobody's taking away what's already there, so keep simming and enjoy
Cheers,
Mark