Urdnot Wrex is the only remaining ME1 squadmate(that is possibly not dead or in ME3) which is why he is singled out.
I doubt he'll be the only special squadmate, since they brought back all voice actors for this.
It's possible, but I mean that it wouldn't surprise me if Wrex is playable in your squad for the combat parts, and then everyone else is just involved in cutscenes/dialogue scenes. Especially since they're talking about how characters won't appear until after you've finished their side missions and that you have to do this after the Citadel coup (eg. after the Krogan arc.)
Of course you can always have a dead Wrex, so...