Doesn't the developer only need to release the source to someone who has purchased (obtained) and used the application, if they ask?

They must release the source to anyone they give a copy of the binaries, which - since the software is free - is anyone who goes to their website and clicks "download."

It's not as simple as "if they ask" - if you choose not to distribute the source code with the binary or provide it for download, you must explicitly provide a written offer valid for 3 years for the source code.

Does including the license in the distribution satisfy the requirement?

I wouldn't think so (you'd need wording like "I agree to distribute source code to you on request to <address>"), but I doubt it's been challenged - it's an obscure use case of the GPL.

Not that obscure; lots of hardware vendors use Linux in their routers/TVs/tablets/phones/etc and distribute the sources separately. In fact, every manufacturer of Android phones should have such an offer included with their device.

Have they done that?

No idea. Have no idea what this software does, why anyone would find it useful, or who is using it.