You could argue the same point regarding Apple's naming of their Macbook line prior to the discontinuing of the original Macbook moniker. Even now, the difference between the standard and the advanced Macbook line (purely on naming) are the words "Air" and "Pro".
I disagree with your point as I don't see any kind of major qualitative difference between an Air and Pro. Both are very similar computers that run essentially the same software - one just operates faster than the other. That's a quantitative difference.
As far as I understand it, a Surface and Surface Pro run completely different types of software. Windows RT cannot run normal Windows Apps. I would view this as a major qualitative difference in the type of machine it is and such a similar naming strategy is confusing and not warranted.
I think they're both actually looking like pretty good machines yet again and both have their uses, but I think the message about what they are is going to be confusing to the marketplace because of the naming. I don't work in branding for a big corporation, so maybe my opinions are wrong. But Microsoft ended up with a warehouse full of unsold Surface RT's last time and I think that this is a big part of the reason why.
The Air/Pro/normal macbooks all run the same software binaries. Microsoft was/is selling two products with different machine architectures that run different software but with almost identical names. That's a marketing and customer-service disaster.
