What's the story, morning radio?

So why is Digital Radio in cars so behind the times?

I mean, if you have a look for digital radios there are plenty of nice units for sale for use in your house. Little speakers, pull up the antenna, cute lunch box size. Perfect for that Sunday morning radio time with the paper and a croissant. But where are the radios in the car?

Today's discussion is thus: if Digital Radio really wants to be successful in Australia, why are the choices of Digital Radios for cars so limited?