According to The Verge (http://www.theverge.com/gaming/2012/8/8/3228247/valve-to-sell-non-gaming-software-on-steam-starting-september-5th) Steam will offer the option to add also other Software than Games.
With Steam updating to a new Version would be much more comfortable.
Now Steam is only available for Win + Mac but Valve is porting Steam to Linux (http://blogs.valvesoftware.com/linux/steamd-penguins/)
The other reason is if we add Nightingale to the Library and Steam-users browse the Steam-Library we reach more people...