He points out that if you're feeling burned out, it's "not the worst thing in the world to try out some other games -- the past couple of years has been great for them."
Of course, he did take the time to remind everyone that there is more to the game than clearing raid content or completing your latest PvP gear set. There are achievements, alts, questing, and tradeskills, to name a few.
While this does indicate that Blizzard is feeling pretty confident in their chokehold on the MMO market, it's also a smart move on their part. There are already enough paranoid conspiracy theories out there claiming that the company merely wants our money, and less concerned with product quality than with elaborate plans designed to trick us into playing longer and shelling out more money.
In fact, GC said this in response to one of these inspired theories.
This reminds me of one of the loading screen tips that urges players to spend some time with their friends outside of this game as well as in it. As Ghostcrawler says, "just check back in with WoW every now and then."