From the user's point of view, I can't think of a good reason to force users to update software, besides maybe a security/privacy issue. As a user, I expect software that works today to work tomorrow--forever. Every time I update, I risk getting a new UI shoved down my throat, or my favorite use case removed or broken, or the app has tripled in size for no discernible reason, or it's now too slow for my computer. I've been trained by software companies' repeated bad behavior to not update voluntarily unless I have some kind of assurance that it's purely a security update and no functionality has changed.

Version your API, figure out how to make maintaining the old versions zero cost, and don't throw users under the bus just because they are (understandably) unwilling to update.

A mobile app is the same as a web page. I view them as much more related to web apps, than to traditional desktop apps.

It’s tied to a backend version. I do get annoyed with apps that want to update every single time, but with auto updates it’s not that bad.

As many mobile apps are merely wrappers around a web app, It’s easy to see how this happens. But I think the end game will be even more web-like: apps that indicate they must be up to date and can’t even be manually set to stick to one version.

"besides maybe a security/privacy issue"

Right - that's enough of a reason for me to include a kill switch!