I agree with the grouping but not with the reasoning.
For example gnome/goblin are both a comical relief (not saying they're ALL about jokes) - also they're small, yes - I guess that helps with the jokes.
Human/orc is the main opposition of the whole damn universe, set up by Warcarft I.
Also if you find forsaken (rotting, missing parts, open wounds, visible bones...), orc or goblin females more feminine appealing than dwarven females (In case you never rolled one, what I assume: they don't have beards) I think there is something up with YOU. And even female troll can only lose to female forsaken in the chinese version of the game. (And after all this is about looks, so everyone has a different opinion )
Dwarf/Troll are rather the secondary opposition in the Warcraft universe (even though it seems to water down a bit recently, not sure if Blizzard still follows that strong dwarf vs. troll theme) and also share a more adult (drunken/stoned) theme.
Worgen/Forsaken both have a fate that they (most of the time) didn't choose (under full freedom) with some of them only tolerating it, others accepting it.