Umm guys, they're just using a model, they're not actually using porn directly. They're using the image of sex, just like Britney Spears, Christina Aguliera(sp?), and many other singers use the image of sex to sell more records, even though their target audience is mostly adolecent females :? but go figure... I guess it makes the guys watch their videos.
From a marketing point of view it's easy to see why M$ is making this move; Japan is a huge market, bigger even than the US one. If M$ can inject some awareness of the product, even if it's by making you look at a sexy girl first, their new console will have a higher chance of hitting it off there, and if they can acheive that, they'll take over the console business. Personally, I don't see it happening though. I've played a few japanese people on Xbox Live, but I bet there's way more on the PS2 Network. Xbox has already surpassed PS2 sales in the US by about 700,000 units and growing, there's no need for this kind of advertising in that market.