If the support comp (a common example in this thread of Riot insta-nerfing OP strats) was truly nerfed in the very next patch because of the fact that it was OP... Doesn't that contradict what Riot has been telling us regarding the time necessary to do balance patches?
What I'm saying here is that I have a feeling that Riot already knew that the supports were over-powered, and Dignitas was just the first team to realize it and utilize the concepts in tournament play.
I think it's entirely possible that Riot many times has already seen that there is an issue with a champ/comp/role/item concept, but is waiting to see if anything ever happens because of it. Other times, I think because the game is so ridiculously huge, Riot doesn't always see things until the widely viewed pro scene discovers/displays it for a large portion of the playerbase to see.
But in those cases, it seems like there is much more time between when Riot notices it, and when they are able to actually do something about it...Urgot was used by M5 in that insane comeback game months prior to the nerf to him...
I'm sure people can always find examples to support their own theories, but honestly, do you really think that blatantly OP concepts should be allowed to remain in the game? OP to the extent that if a team/player utilizes it, all of a sudden their chances of success are dramatically improved over all other known options?