Why do sales number matter at this point? Both are selling WELL above what they were in the previous generation, and thats with almost no new games available at the moment. Its going to be fine. Wii "won" the last round and that did nothing to stop great Xbox 360 and PS3 games being made, and it will be the same with this generation.
Sales numbers greatly matter. Just ask the Wii U. Third-party publishers ignore it. If there is any indication that one platform will dominate another, most developers--especially those with limited resources--will begin making games for the lead platform, either exclusively or first, resulting in long delays of sloppy seconds ports. It's a huge deal. Just ask anyone who owns a Windows Phone.
The Wii is an interesting but abnormal case of a console that technically 'won' the last generation by pure sales alone, but by the end of the generation was completely irrelevant because game attachment rate was abysmal. Basically, everyone's parents bought a Wii because it was cheap and unique, played the free Wii Sports, and then it collected dust for the past 4 years. Xbox 360 and PS3 were the true winners of the last generation because they had enormous installation bases and high game attachment rates. This generation, though, is on pace to be like the 6th generation where PS2 dominated Xbox and GameCube. Not only is that not good for Xbox, as that's hard to recover from, but I think it's bad for gaming because I don't like where Sony is taking the industry (answer: nowhere; just boring spec upgrades). I much prefer what Microsoft is doing (Kinect, illumiroom, etc.), and, as we have already seen with the Kinect unbundling, Sony's success can muck up technological progress by other companies forced into isomorphism due to short-sighted consumers. That's why I'm frustrated.