@ The person who asked about bans.
No, you don't ban people like Ezreal over Shen, do to the fact that as amazing as a carry, that Ezreal is, he doesn't change the game as much as Shen can - Shen can save a carry, can make people focus fire him, and can generally change the game around even if it means he dies.
Ezreal, as amazing as he is, can die without much effort with a little CC or focus fire, because even with a flash ability, you can only run from 5 people and do so much damage at the same time. Losing an underfed carry to take out an overfed carry tips the game in your favor, or at least, lessens their advantage.
Katarina is also more easily countered now with more and more champions being able to break her ult with taunts, stuns and the like, such as taric always being picked, Galio's taunt, and so on - She's viable, but counterable. Gangplank and Tristana counter healing too, but they can do more than that, and are harder to CC (Not sure where they are on the tier list, though.)
@ Kayle - She's still a hard carry, but her moves make less of a difference in team fights now, and if you want a hard carry for damage, Ashe is available.
@ healing - It is useful, but is counterable by not only champions, but items (Executioner's calling), and although it can save lives - It rarely makes games. Siege teams are less of a threat now with the ability to turtle, and the one time a siege team overextends, they'll lose as much as they've gained during one wipe, to a turtle team who has an advantage.
PS @ Kat. - He didn't move her to tier 4, he put her in tier 3. Still viable, just not a rushed pick. She's good, but not amazing. A fed Ezreal can do more than a fed Kat, and a fed Ezreal beats a fed Kat, for example.
Another thing to note - Any champion 'can' give deadly results. It's whether they will or not at high level play, not considering high level team composition.
IE: Kat + Amumu = win.
Kat + Nunu does not.
I will state one last time (Let's face it - this won't be the last time. -Sigh.-)
Tier lists are for champions, not for composition. If you want to talk team comp, find a team comp thread - This is about champions and their abilities on their own without the help of a team. Evelynn with a good team can theoretically rape, but Evelynn on her own is just near unplayable in a ranked game, sorry.
If you see a team with a Taric, Soraka, and Kayle, sure, Katarina is a fine pick, but if you see a team full of tanks and crowd control, why the hell would you take her?