Also, remember that with prepaid you can bring your own unlocked phone (with many carriers).
But those phones don't count toward the total of newly sold phones. And I know it accounts for a large number of pre-paid customers. A few friends, my wife and I are in that camp. Well technically I bought my phone at full price unlocked and then started immediately using it with pre-paid, so there was no previous contract.
"smart" phones don't have to cost many hundreds of dollars though. There is a Samsung one on the market here for under £90 and and HTC one for not much more.
You're right. I did just find some Android devices for around $100 after discounts. But they're years old and locked to the provider. Which is still absolutely valid to compute sales figures, I was sidetracked thinking current and unlocked mistakenly.
From the prepaid companies operating in my area however, I still see that the vast majority of their offerings are dumb/feature phones. And as Tom mentioned, even if they weren't, it's unlikely the totals contribute significantly to the discrepancy we're seeing from these analysts.