It's completely true.
The success of the Hawks is primarily the result of defensive systems, not offensive ones. Obviously they have very skilled forwards that can put the puck in the net, but the bulk of the offense comes via transition, whereby aggressively backchecking, defensively responsible players pressure the opposition, allowing the D to stand up the blue-line, break up the plays, and return the puck in stride to the forwards going the other way.
Likewise, the D is able to jump into the offensive, preserve possession, only because they know they have the defensively-responsible forwards covering their ***** if the team comes back the other way.
While Kane has improved as a defensive player, he is far from a complete player and VERY far from the elite 2-way forward that Toews is. Toews contributes to every facet of the Hawks system, while Kane is just a finisher. A fantastic finisher, but simply a finisher.
One need only look to last year's playoffs for an comparative example.
Both players were relatively cold production wise. When Toews was cold, he was still contributing to the team's success through possession, defense, FOs, even on the PK. Kane, by contrast, contributed nothing when he wasn't putting points on the board. When the two were reunited and heated up, Kane continued to contribute only through production, while Toews battled in front of the net with Chara, continued to be the key shut-down presence on that line against the likes of Krecji and Lucic, etc.
Kane plays his role very, very well. It is a less critical role than Toews. He will always score more points than Toews. Unless he has a revelation as far as his two-way play is concerned, he will not be as important to the Hawks as Toews is.
I am sure he is very important to your Fantasy Pool though. And really, when it comes to a successful hockey team, THAT's what's important.
ETA: You know what, whatever. Don't even bother responding. Chances are most of the people who think Kane is as integral to the success of this team as Toews are the same people who swear up and down that our team defense is perfectly fine. It's the same kind of superficial understanding of hockey underlying both ideas. At some point when you come across people so clearly divorced from reality, the best you can do is pat them on the head and say 'yes, dear. that's nice'.