Why is Nikon not bringing in inbulit dust cleaner in its semi-pro dslr's?

They probably will introduce it at some point, if only to satisfy the marketing department. It really doesn't matter though. Like Fhotoace says: with proper care, you'll rarely get dust on the sensor to begin with.

If you do, just give it a puff of air from a rocket blower.

If that doesn't work, use a sensor brush.

And if that doesn't work, guess what... neither will Canon's built-in system. In those cases, use a (Copperhill) swab.

I have yet seen a Photograph on Flickr with dust on the sensor from a Nikon camera, yet I have with Cannon.

Maybe that the Photographers with the Nikon's care enough to clean them up before downloading them and the Cannon Photographers didn't care, I don't know.

Anyway as I can see that sensor cleaning is not foolproof.

I have 42,000 shots on my D50.

I use it to shoot car races (not the cleanest environment) and I swap lenses all the time.

There is eactly zero dust on the sensor.

The 18-70 has a rubber gasket around the mount (may help a bit), but my other lenses do not.

I would say the answer is "because they don't need it".

write to nikon support to find out