I don't think that's the rationale behind this. If a user is clicking a link to start a BlueJeans session, then it's not against the user's prior wishes anymore

I don't think that's the rationale behind this. If a user is clicking a link to start a BlueJeans session, then it's not against the user's prior wishes anymore. It's the user's current wish to start a BlueJeans meeting and that wish requires the BlueJeans app to continue. Without the "detector", the link click just fails and nothing happens. With the detector, it's determined that the app isn't installed and the user is prompted to install BlueJeans. Otherwise, the app is opened and the correct meeting is started/joined. Nothing is silently done here. That being said, this is still a crappy way to do this. Installing a server is not the solution to this. Browsers need to do a better job of dealing with this and that would get rid of the root issue but, in the interim, these developers need to figure out a better way than installing web servers on everyone's machine. Otherwise, everyone's computer ends up with 10000 of these stupid little single-purpose applications that are always running.