Is it true that for an Icon to be genuine it must sit through forty liturgy's in a church?
No, it is not true that an Icon MUST do so. As far as I have seen (in Greece and here), the “standard” custom is not that it must sit through forty Divine Liturgies, but that it should sit in the sanctuary (behind the iconostasion) for 40 days. Granted, in some Greek parishes, especially during the Christmas Fast, that would also mean sitting through 40 Liturgies.
At any rate, these are all pious customs, of which several others exist. There are several different collections of prayers in various euchologia
for blessing Icons -- and those just in the Greek euchologia
I have in my apartment! (None of which, by the way, actually say anything about having to put the Icon in the altar area for any amount of time). I have also seen slightly different prayers in Romanian and Russian Churches.
Now, one must still ask: Is it profitable, edifying, salutary, etc. to keep some form of this custom? Yup. Personally, I leave my Icons in the altar area for forty days and then ask my priest to bless them with holy water and whatever prayers he wants to read. I just say, "Amen."