> Didn't Apple say basically "if you can sign up in the app, you need to be able to sign up in the app in a way we get a cut". So as long as linode doesn't take on new customers in the app, no problem?

From the press release[1]:

However, Apple does require that if a publisher chooses to sell a digital subscription separately outside of the app, that same subscription offer must be made available, at the same price or less, to customers who wish to subscribe from within the app.

So no, any SaaS that can take on new customers on their site has to give their iOS app the same ability at the same price, with the requisite 30% cut to Apple for those subscriptions. They don't get to choose to not offer it at all.

> Similarly amazon could have a free iOS reader, no problem, from which you cannot buy any books. it's when they want people using the iOS app to buy books but not pay apple a cut that apple is unhappy.

Amazon already has this. You can't buy books from the iOS Kindle app, you can only do it through their website, with a link in the app kicking you out to Safari. That's also forbidden under the new rules (again, from [1]):

In addition, publishers may no longer provide links in their apps (to a web site, for example) which allow the customer to purchase content or subscriptions outside of the app.

[1]: http://www.apple.com/pr/library/2011/02/15appstore.html