The term "Open Source" when applied to these applications is at best confusing and at worst misleading.
While the license of the project may be FLOSS, if all an application is doing is grabbing locally generated input, sending it off to a proprietary third party black box, and then processing the output, the application is primarily glue and the hard work is being done by the proprietary API.
Thus the application adheres to the license of Free/Open Source Software, but not the spirit or motivation, which in this case is primarily independence from third party access to our private data.
By way of analogy, it would be like advertising an electric car that requires a diesel fuel generator inside to charge the battery. Yes, the car may be electric, but is entirely dependent on a machine that only works via fossil fuels.
I've seen a good half dozen "Open Source" applications which work this way and each time it's a bit of a let down.