[Skybird]

And this: I do n ot know how FSX handles this in detail, but in reality, airliners mostly get lined up via autopilot with the runway, but the very last part of approach to touchdown is being flown by hand. That means, the autopilot gets disenagged - but the authothrottle stays active. Can'T tell you whether FSX default knows the distinction between the two.

As said, Wheel Brakes also need to be armed to engage automatically, and spoilers also need to be armed to deploy automatically after touch down.