For me that's the stupidest thing ever for example what if you internet goes down and you making important project in Photoshop that is on Steam (just an example) what happens then ? ...

DeV, you can use programs on Steam while offline o.o That, and there is the autosave, so just save the project first so that it auto saves every 5 or so mins. You wouldn't lose much.

The software is sold by and downloaded from Steam. It does not need internet activity to operate, unless you need an update.