Earlier quoted context omitted.
With launch screen, you mean the new Start screen? All Start menu shortcuts automatically appear there (except if they appear to be uninstallers and such, but those are still searchable and can be added manually). So if you tell Steam to create Start menu shortcuts for a game, they automatically appear on the Start screen.
It seems I doubly-misunderstood the situation. If Steam can still trivially get its third-party-bought programs onto the metro-styled start screen, the popular reporting on that situation was off. And I can't even find a story where Gabe himself actually expresses an opinion on, or concern about, the MS App Store. His comments seem to entirely revolve around Metro being bad for desktop usability and Windows 8 not sel…
All mine are, by default. Valve is concerned about the competition from the Windows app store, not the UI revamp.