It mentions as much on the LX website - no free food for Swiss Economy out of GVA. I would imagine that they see themselves as competing with easyJet & other LCCs out of GVA, ZRH has far less low cost and more transfer traffic. When I have checked LX Y fares seem to be slightly lower out of GVA than ZRH but I certainly would not claim it to be a proper scientific sample. It does raise two points - having a different product out of two airports can be confusing (although BA did it with LHR / LGW), and it makes life difficult for the Cabin crew - other airlines have not tried it for that reason.