The Empire isn't only the Imperials. Many of the Nords want to remain a part of the Empire. It's one of the reasons for the civil war.

That brings up a good point though. Would the loyalists have more Imperials or even other races too in their ranks than the rebels? Would the rebels have some sympathetic Imperials on their side, or even spying for them?

Pax Roma! Bring back the Roman-esque Imperials from Morrowind!

That would be so awesome if they brought back the Roman themed Imperials!

EDIT: good find OP.

Zoomed in really close to the image, and I only have one thing to say... That is a bigass dog. Wait, no, not that. I mean I think that might just be an imperial. Something of the facial features doesn't quite strike me as nordic ethnicity from the elder scrolls. Nor could I say that resembles Bretons from the past.

It looks like an irish wolfhound, which are really big dogs. As for the armor I thought the guys in oblivion just dressed in that style of armor because they were the home guard so to speak. They protected the capitol so they had to look all spiffy with the crested helmets and what-not. From what I've read it wasn't unusal in the real roman legions for armies based in different locations to be kitted out in different styles of armor/uniform. All that aside do we even know the state of the empire right now? The dunmer could be running things for all we know. From the last thing I read the whole eastern half of the continant was in total chaos and the Altmer to the south were trying to consolidate the southern provinces and go their own way. And that's just if the novels are canon. Basically who knows what the imperials look like at this point.