Well the thing is, I don't doubt that garrisons and such make sense for Horde and Alliance architecture looking like orc and human stuff considering when someone says either of those factions names, you think red-roofed spiked buildings for one and blue-roofed medieval/fantasy human stuff for the other.
It's just tiring to see the other races that are part of the two factions not get to show off more of their architectural expertise. Though some of it shows with vehicles.
One thing that really gets me is why there aren't more, or at least slightly more blood elf-looking portions in settlements/outposts/towns. I really like Silvermoon's architecture and am kind of saddened to not see it as much. Would I want to see only that type of stuff all the time? No. But spiky red roofs get old after a while to be frank. Same deal for Alliance. :|
One other thing that would be neat to see is more towns akin to Thundermar in Twilight Highlands, the Dwarf Hobbit hole-types of buildings.