I don't know why the upload feature has been removed from the modern version of Connect, or why a manual upload feature can't be included with Express for that matter?
When activities on my 910 don't automatically upload to Connect, as has happened a good few times already, the only way I can get these activities off my 910 and onto Connect is by manually uploading them using the 'upload' option. If the option to manually upload files is taken away from Connect it will make things very difficult due to the fact that if it doesn't upload a workout automatically it blocks all future workouts from being uploaded.
Also there are occasions where I will use a different device and upload the .gpx file to Connect to keep all my workouts in one place. Removing the manual upload takes this option away from me.
All in all I think removing the manual upload feature from the modern version of Connect and Express is a big mistake and one that should be rectified immediately.