According to several 3rd parties the physical box edition comes with a Microsoft App Store code and if downloaded from the official store the keeping-the DVD in the drive to play is not a mandatory requirement.
There has been several issues with the Steam edition on release with missing Flight Simulator executables and missing files from the premium edition. Steam also takes up to 30% of all sales on its stores.
With the Premium Deluxe version you will also be receiving the 10 DVDs, sleeve, a “Premium Deluxe Guide” for the included airports and aircraft. My recommendations is to purchase the physical version – the DVDs provide a backup and the box and user guides can be kept as a collectable or memento.
The physical edition can be purchased at simMarket (Europe) or from Gamesmen (Australia).