That's how it's made: we know do animated ground traffic using the Addon Manager + Simconnect in FSX, which is very convenient, because the vehicles behave like real vehicles (physic, sound, etc.), not just animations.
And, for traffic on roads, we get it for free in FSX, because whenever you define a road, it will be automatically populated by FSX.
Doing those things in FS9 would require lot of additional work, and it will probably never look as in FSX, and worsen the fps a lot so, we don't port those features back to FS9 anymore, in the more recent sceneries.
