I can make no possible reading of the App Store guidelines that results in this policy - it's clearly new. I guess if Google can't make the Android App Store attractive to developers, Apple sure can. Surely, this cannot be "official" policy, or if it is, it can't be one that lasts more than a couple of weeks. It's not one of those geek-annoying App restrictions that 99% of the iOS target market wouldn't care about even if they knew it - this one affects every end user, and you can bet will be widely publicised by every non-Apple tablet maker.
Realistically, three things can happen to people with App under this policy. Take, e.g., Kindle.
1) They withdraw the Kindle application
2) The add In-App purchasing
3) The add In-App purchasing, but with a 30% price hike
Frankly, 2 is very unlikely - 30% is probably their entire profit margin on the sale. 3 is possible, but makes every Android tablet look vastly better to new purchasers ("The same apps from iOS, but with content 30% cheaper!). 1 is also quite possible - they just EOL it and say "For future Amazon purchases, please grab a Kindle or Android tablet), thus showing a huge chunk of Apples target market a big banner for the competition.
I suppose there's another alternative: that this becomes one of the annoying "Not for big player" rules that they just have a sub-rosa agreement with B & N/Amazon to never enforce. That in itself is pretty underhand.
Overall, my favoured interpretation is this is a re-run of the "Nothing but Objective C Apps in the Store" debacle. Masses of bad press, a dent in developer confidence, and a rescinded policy within a month or two. Apple really are their own worst enemy with this stuff.