Free demo app + paid full app was the first thing people tried when the iOS App Store was new. The conversion rate for that setup is terribly low compare to a 1-click "unlock now" button inside the demo. It's all about reducing friction. App users are busy and distracted. Ain't nobody got time to fire up the App Store, find your paid app and download it (Again???. What's the wifi password here?) just to give you money.
Unfortunately in Apple's App Store Review Guidelines, you have: "2.9 Apps that are "beta", "demo", "trial", or "test" versions will be rejected" Of course, people do have "Lite" versions with fewer features, but I guess there was some vague "threshold of usefulness" that they wanted to impose with this rule. Anyway, although I can find the word in the store, I think its use gets avoided due to this restriction. (And I know the article is about Google, but you used the more generic "app stores" so I'm replying to that)
