I've written about this before. People see that an "average" deck should have between 22 and 25 lands. They figure their deck is average, so they assume it's okay with 22. As more and more people do this, the average deck starts to have fewer and fewer lands. Pretty soon, new players are looking at a statistic that says the average deck has 21 to 24 lands. They assume 21 is plenty and start bringing the number down even more. The average number of lands will typically go down, but the RIGHT number of lands is not the same thing. There are, in a few instances, circumstances where lower CMC cards get printed, resulting in less need for as many lands, but your strategy of finding average CMC should be consistent no matter what new cards or strategies come along. Unless there's significant, reliable, low CMC ramp, I wouldn't even bother worrying about factoring any of that in either.