Why doesnt someone build one portable unit capable of GPS nav, Radar/Laser detection, Satellite Radio, etc etc

I'm just curious why someone doesn't build a one unit does it all. We can't have 4 devices in our windshields. Why don't the major manufactures like Valentine 1 or Escort, Tom tom or Garmin, and XM or Siruis, get together and build one unit you can take from car to car that does all of this plus has a media player for all the video and audio formatas and tons of on board storage. I can envision a GPS Nav screen that uses Valentines ability to point in the direction of an incoming radar signal and even pin point the location of multiple radar/laser sources on the map including remembering where false signals occur using gps technology escort has. Then combine this with a ipod style media player, an competent GPS nav with GPRS updates like the new Dash express.. I mean it would be the end all of all car accesories. They could make a portable and in dash version depending on the customers desires. Wouldn't this be killer?