TSN's Power Rankings have always been pretty awful because it is a mathematical sum of individual fantasy values...which leads to some weird rankings at times. Should always be taken with a grain of salt.
EDIT: Here's the explanation of the rankings:
Quote:
The individual player ratings are generated using a weighted formula that includes the following statistics:
Goals per game, Assists per game, PlusMinus, Power Play Goals, Shorthanded Goals, Game Winning Goals, Shots on Goal, Blocked Shots, Hits, Giveaways, Takeaways and Faceoffs.
Goaltenders are measured using goals against average, save percentage, wonloss differential and shutouts.
As more and more statistics have become readily available over the years, and continue to evolve, the ratings have been tweaked to reflect new and additional information.
Naturally, goals are most important (since there is a 100% correlation between scoring more goals and winning the game) and the scale decreases so that the more peripheral stats are virtually tiebreakers. That is, if you have a pair of 30goal scorers, you would prefer the one that hits more frequently to the one that doesn't. It wouldn't likely provide a decisive advantage but, all other things being equal, would indicate a preference for one player over another.
Arriving at a single rating number for each player simply helps to synthesize an individual's contribution to the collective effort. Player ratings generally fall between 55 and 100, give or take a few points, with the very best players in the league pushing, or occasionally surpassing, 100, while fringe NHLers will be in the mid50s.
So, now that each player has a rating based on his statistical production, the next step is to generate team rankings and I do that by weighting each player's contribution based on their role on the team. Thus, first line forwards count much more significantly than fourthline forwards and toppair defencemen are more impactful than thirdpair defencemen and so on.

http://www.tsn.ca/blogs/scott_cullen/?id=294742
As we all know, many of those stats can be unreliable, or not tell the full story (for instance, defensive ability is not very well captured in those stats), which leads to inherent flaws in the rankings.