I noticed at the dealership that the "04 scrambler 500 has a different shock than the one on my '02 scrammy, it looks cheaper and has no res. Is it a cheaper version or a new improved model?

 

well i think your 02 has fox shox but the 04 is cheeper stuff ... o well ... still a kick a** quad

 

Just one of the few minor changes for 04. I havent had the chance to compare it to my Fox shock though

 

They must have desided to commonize the Rear shocks between the 250 Trailblazer and the Scrambler 500

In 2003 both the Scrambler 500 and Trailblazer 400 came with the rear Fox shock. 250 did not get it.
In 2004, as we are sad to see, Polaris eliminated the 400 and looks to have comonized the rear shocks between the 250 trailblazer and the 500 Scrambler.
If you deside you want a FOX shock you will need to get one from or for a 2000-2003 Scrambler.