This is probably only me, but...
I got FS95, and 98 - These were very similar - No difference in Graphics.
Then Flight Simulator 2000 came out, and was a HUGE graphics step.
Then FS2002 except for the AI, and Auto-Gen scenery there isnt much difference from 2000!
So if you think about it the graphics change in 2's:
(FS95 and 98)
(FS2000 and 2002)
(FS2004 and 2006) - So flight simulator 2004 (If thats what it is will be in a very large step of graphical improvments)
I'm probably making no sense!!
Also I think that the next sim will be 2005!