Get off the DRM launcher bandwagon and I'll buy stuff from the EGS store. Champion it like Jobs did with the Music industry for iTunes.
Otherwise, 1 is enough.... which happens to be well established.
If I can wait for stuff to come on to GOG... I can surely wait for exclusives of newer games to "expire" for Steam. (Which would be patched and most likely discounted by that point)
Bottom line... the exclusives strategy, by itself, won't work.
Get your games from GOG DAMMIT!