No. You can develop one app using either .Net or WinJS.
Remember that .Net apps are interpreted in a similar way to VFP (not exactly in the same way, but for the purpose of this discussion, let's say thay are). The runtime is already on the machine, so you don't distribute that.
>If you want to put your app to Windows Store, have you to develop two apps. for Intel and ARM?
Craig Berntson
MCSD, Microsoft .Net MVP, Grape City Community Influencer