I could be wrong but I think you missed a couple. Sunguard near the lake in the west of Rift, and North Keep in the north of Falkreath Hold. They both look like even smaller towns with only 2 cells.
@ OP: I've been wondering about how these minor cities will be featured. I'm guessing because they are the hold's capital so to speak they must have major guilds and such, but the reason for them being smaller is economic fall in the 200 hundred years since. But that doesn't make sense for them to be physically smaller. edit - Which a couple of them don't seem to be..
As confusing as it was, that Todd Howard quote
“There are 5, what we call, big cities, and they’re all really, really unique. There’s a couple of shots of them. Those 5 are really unique. Skyrim is broken into 9 holds – a hold is like a county and each county is governed by a Jarl, who’s like a King of that county. 5 of those holds are kind of bigger – they have big cities – while the other 4 have smaller, what we would call, like a town. A little bigger than but like that. So towns, we have 8 or 9 of those.”
seems to suggest they are fairly large, the major towns of each hold, of which there are 4 (I haven't been able to conclusively figure out where that last hold is BTW). Going by this: "while the other 4 have smaller, what we would call,
like a town. A little bigger than but like that." So yeah, I guess they have a castle of some kind, if they're where the Jarl of the holds live. Maybe they'll be a bit like Caldera in Morrowind.