The Colorado Avalanche are one of a number of teams making a splash early this season (and consequently climbing up these rankings). Toronto, San Jose, St. Louis and other clubs are also enjoying early success.
The trouble with early success is that, because there is so much chance in hockey, almost anything can happen in a short span. Toronto and Colorado have both had hot starts in very recent memory. In 2011-12, the two clubs combined for a 9-1-1 record early in the season; both would fall well out of playoff contention as the season wore on. San Jose's experience is even more recent. They crashed and burned last year after a perfect January (though they rebounded late in the season).
Without a crystal ball, it's not possible to know with any certainty which teams will collapse. But a good method for keeping expectations realistic is to identify things which can't last–goalies playing over their heads, teams winning despite getting hammered on the shot clock and the like.
That's one of the primary objectives of these power rankings: to try and identify those warning signs.
Unless otherwise noted, statistics come from NHL.com and are current through Sunday's games.