Automakers are starting to get hip to this fact. Hyundai, while they're offering integrated nav on the Veracruz, sees no problem selling Garmin aftermarket units right off the showroom floor. The portables are a fast growing segment as consumers realize the value of third-party, portable nav systems. Portable navs are less expensive, offer features that cost a lot more on factory systems, and are upgraded far more regularly. For $1,000, you can get a system that offers real time traffic and weather data, works with bluetooth phones, and can be even more functional with the addition of optional software cards.
Not only are the aftermarket units cheaper, they're portable, so you can use them in whatever car you please. Of course, luxury buyers being who they are, there's a certain need to show off that a factory navigation system fulills, but puffery is costly. The quick path to obsolescence that all in-car electronics take means that very in short order, you've got an expensive, unfriendly, limited hunk of LCD-interfaced crap in your dash.
[Source USAToday via Kicking Tires]