Nonsense, Beijendorf; you got a bad RT that you had to return. Mine has always run flawlessly, first with 8.0 and now 8.1. We also have the Pro, and the main advantage to the RT is the 2-3 days of battery life using it mostly to browse, stream videos, and play music.
The advantage to producing multiple devices is to sell to consumers in different segments/ at different price points. A major difference in the Pro 3 release is that it is available with/at a broader range of specs and prices, although not as low as the current RT/2 levels. I did not read or imagine as much into the Surface Pro 3 release statements as you did. I have 2 college students happy with all-day RTs and was surely happy getting each expandable 64GB unit, loaded with MS Office, for $400 at an MS-store-opening sale last summer.
BTW, all Surfaces have been tablets; Microsoft has produced only tablets.