I believe a large airline that likes to write their own manuals has written that for planning purposes they'll consider a VOR/NDB/SRA etc and not a LLZ only approach to a runway which is served by a Cat I ILS at best. Makes perfect sense to me, however as others said I think the legal interpretation does allow you to use LLZ only, seems to me like a 50/50 chance whether it's the LLZ or GP that will fail if there is a failure so I'd rather have my plan B based on a totally separate aid thanks.