Romans wore Togas.
And the armor looked nothing like Roman armour, nor did the architexture, asside from the fact that it didn't look like it was about to fall over; unlike the other cities.
Saying Romans wore Togas is like saying Americans wear Tuxedos. Most ancient romans wore tunics, or a variant thereof.
On your second point: The architecture of Skingrad and the Imperial City strongly resemble the architecture seen in the Holy Roman Empire, as do the Imperial Guard Armors.
If anything, the Ancient Roman style Armor in
Morrowind is the aberration. While it made sense in
Redguard (Being 200+ years before the other games), the rest of the series has the Cyrodiilic Empire as being more like the Holy Roman Empire (A.D. 962- A.D. 1806) than the Ancient Roman Empire (27 B.C - 476 B.C.)
Unfortunately, the Holy Roman Empire was so much more awesome than the original Ancient Roman Empire it's been endlessly copied in fantasy settings to the point that it's become the "Boring Standard Medieval Fantasy Setting".