The iPod: not just a passing fad.
90% market dominance is all very well, but when half the cars destined to be sold in the USA in 2009 offer iPod connectivity it's a fair bet that the iPod isn't going to die out in a time frame of less than a decade. It's the new cassette tape, and that lasted for nearly four decades: even taking into account the faster turnover of technologies I reckon being built into cars means it's going to be around for another 5-10 years minimum &mdash one to two generations in the automotive world.
Cars have a much longer after-life than consumer electronics, and most folks don't bother replacing/rewiring their in-car electronics (especially as they're getting more and more tightly integrated into the vehicle). So even if something new sweeps the iPod out of its dominant position in the post-Walkman mobile music market, they're probably going to stick around (in one form or another) as a cartridge medium for carrying music to and from your car.
Cars: the ultimate iPod accessory.