Which could have been easily explained via a name change.
The only example I could think of is a 4 cylinder suv. Looks the same drives different and can't pull what you're used. Call it a crossover, boom sales success.
In a way this is already the case. Crossover would be the classification of the product in your vehicle analogy, but not the name of the product. So to bring this back to the realm of the surface RT, it is classified as a tablet and Microsoft has marketed it as such. If anything, the surface Pro is being mislabeled as a tablet since it has more in common with a laptop, and this is where the confusion comes from. Microsoft released two "tablets" with very different capabilities. Surface as a brand would/will make a lot more sense when it involves more than two tablets...for instance if/when a surface phone is released and a smaller gaming tablet.
Going back to vehicle analogies, think of the Honda Civic sub-branding. You have DX, HX, EX, ES, S, SI, SIR etc ... mostly meaningless, but it lets a person know how the amenities and capabilities of the various Honda Civics differ. The only reason "RT" doesn't make sense is because it is new, and the pool of sub branding is currently very shallow.
Like I said before, we just need to wait a while and everyone will know what "RT" means, it just has not had sufficient time to define itself.