Why? Why do Sony care if XB360 is outselling them? As long as they have a large enough install base that it isn't ignored, the fact they're being outsold isn't as important as turning a profit. Case in point, both companies are being trounced by Wii, but neither really cares. They aren't rushing to cut prices to compete with Wii. Losing hundreds of millions to gain sale parity wtih XB360 isn't worth it, if selling less will mean a long-term profit.
This isn't a race. It never really was. It's companies trying to turn a substantial profit and balancing prices with profits with sales to hit the sweet spot.
This may be too early to be talking about this, but Sony should care that MS doesn't get too ahead of them this generation. When the next generation launches, assuming price, network, services and technology is comparable, I believe most consumers will go with the company they're used to.
When this generation started, there was a lot of my friends that wouldn't get a 360 because they weren't used to the controller for Madden. Most of them have converted to the 360, partly due to lower price and partly due to Live. I know I've heard it from Sony several times that the brand recognition would compel gamers to buy the PS3 despite its price simply because it's a Playstation.
Remember the "It would still sell even if no games were released at launch comment". Those converts will now have to be won back by Sony and it seems pretty evident from the investment that MS has put into the Xbox brand that it may be even a tougher fight for Sony the next round.