We have updated our review of the Road King Series II to include information on this engineering change:
http://www.musicplayers.com/reviews/guitars/2006/0906_MesaBoogieRoadKing.php#comments
(if you read the review before, skip to the Other Comments section)
New Road King Series II amps will be (or are) shipping with the Tuner output if existing inventory of RK II circuit boards are exhausted. This feature required a change on the circuit board since it involves routing audio to a new output, so unfortunately, retrofits/upgrades are impossible due to the complexity of the change.
Basically, there was the RK II. Then the Roadster came out, and people liked the Tuner out, so the feature was rolled into the RK II. There are no other changes to the amp.
Not a big deal in the grand scheme of things. There are numerous ways to send a signal to a Tuner and keep it out of your signal chain.
Scott