Okay, I know what everyone is going to say "They have Manta's, why would they need Titans?"
Well let me frame it like this. Has Air support ever held ground. Has it ever pinned a battle line together. Has it ever taken up a defensible posistion and fought to the last.
No.
The annoying thing about something that is flying is it inevitably has to move on, and if it can hover, well it inevitably gets shot down unless it moves on.
So with that in mind, while Manta's can fight Titans, they don't fill the role of titans. And are not as accessable to the game as the other races titans.
Humans (Imp and Chaos): Titans
Eldar (and I am sure DE have some, revenants are FAST): Titans
Orks: Stompas and Gargants
Necrons: Well, pylons and monoliths are fluff wise suppossed to be super huge. You all saw the Dark Crusade intro vid. And I wouldn't categorize them as one of the Battle Races as the others are.
Tau: Nuts
So, why don't they have a large battlesuit. With all their glorified technology, wouldn't they make one.
I think they would. Sure they make Tiger Sharks and Mantas to deal with Titans, but a Thunderbolt squadron can easily deal with them. On the otherhand, a Baracuda squadron can't easily deal with a Imperial Titan.
Tau could easily make big Battlesuit. Mount those cannons that are on a Manta on it and such.
Okay, now for Super Heavies. This is a bigger problem than the lack of a titan class. They have nothing to equivalate to the Baneblades and the like.
While fluff wise this kinda makes sense, games wise it is unfair I believe. They need some sort of big tank. Yeah, once again people can site mantas and tiger sharks, but once again $$$ is an issue in gaming aspects. And many of the same arguments that I applied to a titan apply hear in terms of holding ground and such.
Okay, while I wouldn't advocate Star Wars Tanks as super heavies, lets head in this direction at least.
I guess you could use IG super heavies as Gue'vesa tanks, but that is a little cheap to force a Tau player to do that.
So I may be alone on this, but I think they should have these things, almost for game purposes rather than fluff purposes.
POLL RESULTS
Should Tau have Superheavies/Titans?
Yes, they need both. Its fluffy to me. 7 (36%)
Yes, they should have both for game purposes 4 (21%)
Yes, they should have superheavies. 7 (36%)
Yes, they should have titans 1 (5%)
No, they should not have titans. 4 (21%)
No, they should not have super heavies. 1 (5%)
No, they should have niether. Ruins game balance. 0 (0%)
No, they should have niether. Not fluffy in the least. 2 (10%)