No, Modern Warfare 2 is still a supported multiplayer game. I'm guessing you had some type of network issue or encountered some sort of bug.
Modern Warfare 2 is still among the top 10 multiplayer PC games on Steam at the moment, going by the Steam Game Stats - today its peak players was double that of Black Ops, but nowhere near the amount of players of MW3.
A recent Major Nelson blog post shows that Modern Warfare 2 is still among the most played multiplayer games on Xbox Live as well. (Also note that CoD4 and WaW are still supported games...)
There was some talk of shutting down the Black Ops servers on PSN a while back, which I believe was a reaction to the rampant cheating/griefing that occurred after the Playstation 3 firmware was hacked. However, I do not believe a shutdown actually occurred.