While you do NOT need an iPhone/iPod to listen to a podcast, when you do have a podcast you now have the ability to listen whenever you want (buzz word “time shifting), and you can listen wherever you want.
In a recent article at techcrunch.com, they reported that apple has sold 51.15 iphones since it was launched. Apple has just announced that they managed to push roughly 8.75 million iPhones out the door in the second fiscal quarter of 2010