On topic: I personally agree that the ilvl requirement set by the creator shouldn't exceed past his/her own average ilvl. It makes sense and would be fair to the people joining up said PF group.

Off topic on ilvl: My thoughts runs along the lines that content can certainly be completed at the minimum ilvl, but you have to be spot on to the T with all the mechanics. Very little, if any, room for error. The higher you shoot above the average ilvl, the greater the margin of error for most mechanics (notice I said most, and not all). i.e. Faster completion times for dps checks, greater capacity to soak up damage, healers can heal for more, etc. Asking for ilvl 78 in a minimum ilvl 50 is just asking for an easy run with 0 challenge.