One being an arch difference , isnt the same as whats commonly seen going from DT to mobile, which is primarily clocks.
Seeing th the differing clocks is somewhat acceptable, whereas, a total different arch is not. The performance is always going to sway to the DT variant, thats a no brainer, but saying its something its not, as in a 280 having anything to do with the 280m, thats open for a legal discussion, and not in nVidias favor, just going by precedence alone, which again, is accepted as the norm. Naming ones gfx card in YOUR (nVidia/ATI) particular power rankings has little to do with the actual parts used, but if youre hoping for some realiability in the future, dont hang one on the folks by using a different arch, and saying one is close to the other just isnt so.
So, in all fairness, using a downclocked card is seen as the norm, as in ATI's case, as well as in some of nVidias, but to lump it all together, and nVidia using a differently named arch just isnt right, as one has been accepted, while the other transcends to , like I said, a libelous scenario