Actually you're wrong on both counts. Jamar Fletcher came in and started in relief of Sam Madison and faired pretty well for a rookie CB.
And on the second count, Santana Moss came back into the lineup in week 8, and though the coaches were very hopeful that he would make an impact, he did not. He still had half a season to break into the rotation and make an impact, he still failed to do so, whereas Chambers made waves immediately. This is not his rookie season. His rookie season is over, and it was a disappointment. WRs rarely make waves in their rookie years, much like CBs, so he has a decent shot at improving.
Rod Gardner in my opinion will be mentioned among top 10-15 WRs for many years.