No in terms of scale all we have to go by is that they are all as big as the Imperial City and I think if I am not mistaken one major city is twice as big.
:facepalm: Okay. I'll say it again. THERE IS NOTHING THAT SAYS EACH CITY IS AS BIG AS THE IMPERIAL CITY. If you wish to contradict me, please provide a source. I will also once again explain my reasoning for saying they are smaller more concisely.
1. Todd has said Skyrim is "Roughly the size of Oblivion".
2. So far, Morrowind, Oblivion and Fallout have used the same sized cells, so the tradition will probably continue.
3. The map of Skyrim from the behind the scenes video has a grid, which is probably the cells.
4. Assuming they are cells, as is probable, they number roughly 4400 on that map.
5. If the cells are the same size, they have roughly the same numer as Oblivion (4600) which makes it "Roughly the size of Oblivion".
6. I have compared the cell maps of Oblivion and Skyrim on an equal scale (I stretched the map so the cells were equal in size when compared).
7. In this comparison, I discovered that the outlines of the cities in both maps took on average, roughly the same amount of space.
8. They are probably roughly the same size.
Hope that was clear enough.
Edit: seeing your edit, I will restate that. They would still call it "massive" if it took up less space than Bruma, because they want to raise the hype.