It's a fairly common practice to take 1% crit chance runes on anyone, be they mage, ADC, fighter, assassin, etc. The reason is that the 1% will actually show up more often than 1/100 auto attacks because of how Riot implemented crit. That 1% early crit chance can really mess up the early game, there's not much that can be done against it, and there's almost no cost to doing it because no other single rune will change the tide nearly as much.
That's what Meddler is talking about trying to remove. People trying to game the crit system for an early advantage.
Yasuo wouldn't be effected by the changes because he's actually building crit, not trying to cheese an advantage off of 1% crit chance. If they remove crit chance runes, Yasuo would likely replace them with crit damage or AD runes and be fine.