Well if you think about it laptops that can output to 2 screens is an easy task when it comes to displaying a desktop or watching a movie while typing a document. But if you are talking about playing a game at a high resolution on 2 monitors then it is a little more difficult. The thing with games in todays market is that it is not just displaying an image on a screen. The GPU does pretty much all the calculations besides the physics, ai, particle effects, and some other basic code. But when an image is rendered the GPU looks at textures, lighting, layering, and colors for millions of pixels over 20 times a second. This doesn't like much but it is.
I remember back in 11th grade in high school I took an animation class with maya which is used by a lot of game designers. I created a simple space scene of a ship in space passing a planet. I remember when trying to set the camera angle I would render a small 480x640 with low quality and it rendered like nothing. (Was using a fast studio 256mb GPU in the tower not the render farm) But when I tried creating a image at the resolution that would display on a 1080p tv, it took a little over 2 seconds. And it didn't have to do any fancy particle rendering or anything.
And to do videos was worse. It took about 2 hours for me to render a 4 second clip at 1080p but I think about 40% of the time it took went into the compression.
But hey sony might create a ps3 slim or something that can do 2 HD outputs. But for now it is the hardware that limits it on the current ps3's.