I mean, it's not that unethical; that's a big word to be throwing around. It's just kind of a dick move.
You're pretty much describing the foundation of science: breakig stuff that's working just to see what happens.
That said, I don't think I'd call this particular experiment unethical, because it was a free mortgage calculator app and I can't imagine people depending that much on it. Calling it a dick move seems more apt. Then again, who knows...
Why does a site like reddit want to push their app so badly? What can be done with an app that can't be done on a webpage now and what is so important to something that just delivers text?
Companies push their own apps for control. They are very limited on the types of metrics and tracking that can be done through the browser. By pushing their own apps they become limited only by the operating system itself.