Most paid for apps (though not all) sell exactly the same analytics that free apps do - why turn away an extra revenue stream?
Unless the developer has committed to not selling your data, they probably are already doing it.
Exactly.
I had invested time in Spool, and when they got acquired by Facebook, all I got was a bookmark list in a mail attachment and no more service. No readable article, no offline video, etc.
Even paying apps go for for a sale, less often though. For me Pocket is so seamlessly integrated with my online presence that it will of course to see it go(considering acquisition will kill it or somehow make it unusable - ad etc) but the ease/swiftness makes to very hard to switch to any other service paying or non-paying.
One example is their Android focus which, sometimes I funnily think, developers like Marco despise(no, read ignore :P ).
Instapaper's Android app, while not done by Arment himself, is probably the most pleasing non-Google Android app that I've used. He may not care about the platform, but he didn't push a poor Android product.
And those acquisitions work out so well for the product, especially smaller, more niche products.
If they've taken that much money, they are going to have to provide a strategy to monetize. If they are doing it for free, it means they are selling analytics about what you are reading to somebody else.
For myself, I'll pay for the app.