I think it is essential to have this as a setting. Consider a setup where the pvr backend is not on the same box as XBMC is. It is IMO not a good idea to activate (or even hardcode) the prevent-shutdown behavior for this scenario. You most probably have no the intention to prevent shut down of the *XBMC box* in case the *PVR box* (on the other machine) isn't idle, right?