The only thing that is not the same is Draenei and BE being available in the pre-patch and the option for people to remain in classic, which at the end of the day is equal to those people stop playing the game because they don't want tbc.
Other than that it's the same natural progression from vanilla to tbc. Otherwise they would just have tbc without access to classic zone and everyone starting in hellfire .. that's the only way starting all chars and 58 would make any sense.
The 1 time boost is there to increase the sub count of course.