Getting new gear seems like a problem for the player that's unrelated to the argument. In WoW a tanking paladin has a completely different playstyle and armor than a healing paladin. That doesn't stop people in their tracks .
There's a substantial difference between changing between a healing paladin and a tanking paladin in WoW and going from a Shadow to a Sage (or vice versa). The paladin, regardless of spec, maintains a constant and standard suite of skills that all specs have available to them. They also use the same type of gear, regardless of whether they are heal or tank or dps (all of them wear plate armorWhile the playstyle and the gear are different, there are still the same standard abilities. Sage to Shadow have roughly half of their abilities changing, coupled with a vast difference in how their resource operates, which creates a vast gulf in how the two different ACs play. The different specs in WoW still follow a roughly similar playstyle: rogues are all much like rogues, warriors like warriors, etc. A Sage and a Shadow play, from the abilities they use to the actual way in which they manipulate their resources, in completely different ways. Leveling to 50 as a Shadow does nothing to prepare you for how you play a Sage: the abilities are all different and the way you use your resources is all different. The same applies for every AC pairing for their base class: Scoundrels and Gunslingers have the vast disconnect between Stealth + Upper Hand and cover; Sentinels use Zealous Strike as their primary Focus gain whereas Guardians use Sundering Strike (not to mention the difference between using heavy armor for survivability compared to medium armor and massive amounts of powerful low CD survivability CDs and the addition of Centering stacks). About the only class that you could feasibly do it with is Trooper because VGs and Commandos both use remarkably simple playstyles with little difference in fundamental playstyle between the two.
Respecing AC is vastly different than respecing your skill tree. With a skill tree respec, you still have the same fundamental class that you're keeping: the same default abilities and the same resources. With an AC respec, you would be changing more than half of your default abilities (re: the ones you actually use as part of your primary rotation rather than those that just get tossed off your bar because they're not useful) along with a substantial alteration in how the class operates on a fundamental level. As such, they're not really anything even remotely close to the same thing.