From a consumer stand-point, once the Helix intiative gets made official at E3 (all 1st party published MS games are now going to launch day & date on PC as well as Xbox), I do feel that one of the incentives that pushed people towards getting an Xbox hardware does become somewhat dulled. However, for MS, this makes way more sense in the grander scheme of their business.
However, for things like Scorpio, it does become somewhat of a factor. The truth is, we've never had a console where it didn't have a form of an exclusive library to help sell it. The Xbox platform is going to be the first to attempt this, and there is obviously a ton of risk involved. It also allows people an opportunity to join or become a part of the Xbox platform without having to actually own an Xbox, which for MS is way bigger of an opportunity.
So no, I don't think this causes people to leave the Xbox platform, so much that it allows them a chance to abandon the hardware side of Xbox while still maintaining their software portfolio that they have established without having to stay on Xbox hardware when the time to upgrade comes. Now that both hardware manufacturers are going to be asking users to buy into the iterative model, it does create an opportunity for users to leave the Xbox hardware without losing anything.