Following Apple's iBooks Author announcement today, word started to circulate that content made with Apple's app could only be sold in Apple's iBookstore. Authors could freely distribute their work, but they couldn't sell it elsewhere.
After digging through the licensing PDF, Leanna thinks she might have found the pesky paragraph in question, namely, section 2.B.(ii).
If your Work is provided for a fee (including as part of any subscription-based product or service), you may only distribute the Work through Apple and such distribution is subject to the following limitations and conditions: (a) you will be required to enter into a separate written agreement with Apple (or an Apple affiliate or subsidiary) before any commercial distribution of your Work may take place; and (b) Apple may determine for any reason and in its sole discretion not to select your Work for distribution.
It wouldn't be unusual for Apple to exert this level of control over content, but that doesn't make it any the less irksome. Given the pushback they faced following subscriptions, if this isn't an error from the outset, Apple will need to walk it back