Inc Wall of text. Since this hasn't been said for quite a few pages I thought I might as well say it since the QQers are back. The tier list compares the champions against comparable champions. For example, since he's been coming up so much, Cho'gath. Compare him to other PURE tanks, Shen, Galio, Amumu, Rammus, Allistar.
Amumu - Stun, AoE bind, massive AoE damage
Shen - AoE taunt, Heals others, Shield
Galio - AoE taunt, fairly large AoE damage, shields others
Rammus - Taunt, AoE damage, Small knockback + slow
Allistar - AoE stun + Knockup, Knockback, AoE heal
Chogath - AoE Knockup, AoE silence
All of them have something that FORCES the target to target you, rather then a minor annoyance.
Now lets compare him to the Offtanks - Nasus, Garen, Sion, Xin Zhao (depending on build), Udyr, Gragas, Singed, Nunu, Mordekaiser, Malphite, Blitzcrank.
Nasus - AoE % dmg drain, attack speed slow, AoE armor /magic resist reduction
Garen - AoE dmg, silence, % dmg reduction
Sion - Reliable stun, AoE nuke, Reliable self heal
Xin Zhao - AoE % dmg nuke, knockup on short CD, AoE slow
Udyr - AoE dmg, single target nuke, self heal / self shield, Reliable stun
Gragas - AoE dmg, % dmg reduction, AoE slow, knockback
Singed - AoE dmg, AoE slow, Throw Back
Nunu - AoE dmg, Slow, Speed up ally
Mordekaiser - Shield, % dmg drain, AoE dmg
Malphite - Shield, Slow, AoE knockup, AoE attack slow
Blitzcrank - Grab, Knockup, AoE Silence
Chogath - AoE silence, AoE Knockup
Again, falls short of the others, who have more reason to focus.
Now I understand some say "Well then just play him caster". Inc second wall of text.
Annie - 2 AoE nukes, nuke, shield, reliable stun
Anivia - Nukes, 2 AoE nukes, stun, wall
Morgana - Nuke, AoE Stun nuke, Shield, magic resist reduction
Veigar - 2 Nukes, AoE nuke, AoE stun
Kassadin - Teleport, AoE nuke, Nuke silence
Karthus - AoE nuke, Nuke, AoE dmg, slow
Ryze - 2 Nuke, Snare
Fiddlesticks - AoE nuke silence, AoE nuke, drain, fear
Cho'gath - AoE silence, AoE knockup, Nuke
To be fair, if you were AP Cho'gath, you better be playing like AP Sion, AP Gragas, as an offtank having SOME survivability. Still, compared to others he falls short thats all. You may enjoy him. You may do well with him. All it is is that if you wanted more utility, you should be picking a different champ. Just because your champ is low, doesn't always mean they're terrible, all it means is theres always a better option then them.
Edit : And yes I realize that this is on the front page, but most people look at the tier list, see their champ is low, and rage. They only read the responses, rather then Elementz's full post.