Well, since you feel free to use your family as the standard for all of society...
I did? that's news to me!
Look - I dislike receiving lines (both at funerals AND weddings) for this very reason...because where is the line drawn between who is receiving and who is being received?
With some of my family members, the guy who fought alongside my grandpa in WWII would have had to have given his condolences to approximately 60 people back-to-back if the people "receiving" was made up of spouse, kids and grandkids (nevermind adding in his still-living siblings). When my BIL died 18 months ago, I STILL don't know how many people considered themselves "immediate family" (Irish-Catholic family from "the old country"...I know he had upwards of 110 1st cousins). For this very reason, there was NO receiving line at either.
But if they HAD a receiving line and didn't want to have 60 people lined up to accept condolences and I had to wait in line? Then yeah - him being my gramps or BIL takes precedence over you (general you) hanging out with him at Bridge Club once a month.
Not that I get to arrive 1 hour after visitation starts and say "Hey! I'm family - move aside!"...but if I get there and see my sister in line, I'm going to go up and stand with her. Likewise, if I am standing in a receiving line for my boss's father or neighbors grandmothers funeral and one of their family members wants to be with their other family in line in front of me? I don't consider it an etiquette problem.
It's a funeral...it's neither the time nor the place to be looking to find offense. It just is what it is.