Alright, that "Top Tier" is the Broodlord, Carrier, Battlecruiser trio, just sayin'.
As for the topic. The Ultimate is one of the special traits of the Protoss that Blizzard tried to make work.
In my opinion, it didn't work out so well, but that's just me. The whole idea behind starcraft is to have three quite different rances against each-other. No mirrors. Well, no straight-angleled ones, anyways. Even if giving everyone an Ultimate would be a good idea, I doubt Blizzard would go with that, given how even their current one isn't used that much.
While I DO agree that Zerg are lacking somewhat to the other races diversity-wise, I'm hoping the expansion will fix that. ^^
As for Nyduses, they're cute, but I stoped using them past Beta. They just don't seem to be worth the effort that much...