Because they have convinced people to purchase iPods (> 2 gig capacity) en masse. Heck, they even almost convinced me to get one (I own a Sony NW-E407).
At 192 kbps, 100 mb ~ 1 hour of music
Therefore, 20 gigs ~ 200 hours of music.
Yet with the longest rated battery life in the iPod family, the iPod mini lasts only 18 hours. Of course that’s assuming ideal conditions (i.e., low volume, hold switch left on, no EQ, 128 kbps mp3’s), but we’ll let this theoretical situation to occur.
18 hour battery life = 18 hours of music * (100mb / 1 hr @ 192 kbps) = 1800mb
4 gig iPod mini * (100mb / 1 hr @ 192 kbps) = 40 hours of music.
Even with Apple’s theoretical battery life, there’s no way you can listen to even half of the songs stored on your iPod. Eventually you’ll have to recharge your iPod and during this dead time, you can easily upload another 4 gigs of music onto your iPod (6.3 MB per second over usb 2.0)
But I suppose a lot of iPod owners are top 40 radio people who either a) listen to albums with 4-8 mins of goodness followed by 52-56 mins of filler or b) singles.
For case A: Even if the albums were heavy on filler, there would likely still be enough 15-25 hours of good music on a fully loaded mini. Even then, it begs the question: why don't you delete the filler?!
For case B: Since you are making specific song selections, you likely enjoy the songs that you’re uploading on your iPod mini. Therefore you will have ~ 40 hours of music on your iPod.
Thus far, this analysis assumes that the user will only listen to their songs once only to never listen to them again. And of course, this rarely happens. In reality, from what I hear, the iPod lasts anywhere between 6-15 hours. Not to mention, that the battery capacity slowly decreases over time (the batteries are lithium ion).
Until the battery life is dramatically improved, it’s quite clear that any iPod with > 4 gigs is a superfluous purchase.
I’m surprised Steve Jobs hasn’t started selling shit in a box for $200; I’m sure it would become a best seller with the right ad campaign.