If you consider it a Tablet, they maybe on to something, thing is, it's not and shouldn't be compared to other Tablets out there.
Try Pricing and things change quickly! How many Tegra/SnapDragon tablets can you get for the price of a i7 Surface Pro 3?
It is a tablet form factor so there for that statement is true. As a tablet it is the fast and most productive. Price is not a factor in this statement. Price has nothing to do with this at all.
I think this is Microsoft's finest advertisement. I guess it just comes naturally when you have a great product :P