...But seriously, the price doesn't change much from launch to replacement. Then again, I could be wrong. .... ;p
They do fluctuate. Lets take D90 kit as example.
When just launched it was selling over 1800. Later around mid-life (1 year) it was selling for 1650-1700. Since middle of this year, D90 kit is selling for around 1450.
I would call that change.