Welcome to MobileRead, toria!
I wouldn't read too much into Amazon's not saying how many they've sold -- nobody really talks numbers on these devices.
In fact, you've got me wondering if PVI (the folks who manufacture the e-ink displays) might not have their customers under some sort of non-disclosure clause that prohibits them from talking specific numbers. PVI has been so hush-hush on details, they may just not want the actual capacity of their factory to be common knowledge.
Just an idle wondering, that. Don't take it for more than it is.