Yes they are joking... We always argue about which color is faster. Of course, one look at mine, and we know which color is really faster..

Triumph claims there was a power increase when the Roadster came out, along with stronger clutch and drive train parts. Realistically, the power increase probably came from the exhaust change, and any slightly modded older Rocket will have no problem keeping up with a Roadster.
Any Rocket of any year, with relatively inexpensive mods, will put out about 150 HP / 150 lbs/ft of torque. If you want more, it will start costing ya. Mine sits at 140 HP/ 142 lbs/ft at the moment, with an air filter change, I could reach the 150s, but I'm pretty happy with the way she runs right now.
Most of the differences have already been listed.. In addition handlebar clamp/gauge mounts have been changed, in about '06.. The early '04 Rockets have a slightly different oil pan than newer Rockets with drain plugs located in different locations.
My 2004 Rocket III Standard just turned over 70K miles this weekend, with no internal changes other than the output shaft bearing, which was an early recall issue. At 70K miles power has not declined at all, the transmission shifts smoother than ever. It is really running great.