It's not greed, it's keeping the profit margin. Have you noticed how the original iPhone and the iPhone 4 both cost the same (at launch day) [yes, I know Apple lowered the initial price for the iPhone "1", but it has stayed the same since then], but beefing up the machine with more power, more memory and more more?
Also, I think Apple likes to put design before function. So if a USB host component might cause an increase of 0.05mm in thickness and it just doesn't feel thin anymore to his Jobsness, they'll can it and sick R&D on integrating USB with whatever chip they think could handle a few extra layers.
USB Host on an iPad would make a lot of sense, as it would on an iPhone. I would like to be able to download images from my camera onto my iPhone ... photo bucket in your pocket
