I had exactly the same happen to me, 10k miles was a step change as was 15k. Very strange, more responsive, smoother with no morror shake at all now apart from the stereo and also added a few to the mpg. I put it down to the service though rather than an in built change, it could be an in built run-in period so as not to stress the engine when new.
My recent injector work and remap has also changed the mpg and amazingly the car refuses to drop below 40mpg as an average (tank or normal setting) with pretty much 90% short trips! Can't wait till I hit 30k miles to see what happens then, only 6k to go