They do try to synchronize that stuff on champions.
When Teemo gets updated his skills will more than likely move around (as you stated, he's super old).
Here's the AskRiot on it:
http://euw.leagueoflegends.com/en/news/community/q/ask-riot-runes-splash-art-and-buttons
Q: How do you decide which abilities get assigned to which buttons?
A: There are a couple of guidelines we try to follow with ability slotting to help players when they’re first learning a new champion.
First, if an ability is shaping up to be the bread-and-butter spell, the one that’s cast most frequently and ranked up first, we tend to assign it to Q. While players will eventually try all kinds of skill orders, we try and make sure that for a player trying a champion for the first time, maxing Q is a decent choice.
Second, some types of abilities have trended into certain slots, and we try to follow those trends. When working on Kled, for instance, we were prototyping an early version of Jousting, his dash ability. We looked at similar melee fighter champions like Riven and Yasuo, saw that their dash abilities were in the E slot, and followed suit with Kled’s dash. Similarly, his purely passive attack modifier, Violent Tendencies, has similarities to abilities like Vi’s Denting Blows and Vayne’s Silver Bolts, which both live in the W slot.
By following existing trends, we can leverage skills players have already learned from other champions to help get over the hump of playing an unfamiliar champion. It’s similar to how games in other genres follow shared conventions - if you’re playing a new, complicated FPS, for instance, you at least know that pointing the cursor and clicking the left mouse button will (generally) shoot your gun.
Oh, and we like putting ultimate abilities on the R button. It just feels like the most powerful letter, you know?
Harrow, Game Designer