Really? My partner's stepfather (who re-married several years after his first wife died of cancer) is the most decent bloke you could ever hope to meet.
You have missed the point.
Today, any bloke that moves in with a woman and her baby is referred to as a 'stepfather' for some unknown reason. They are never 'married' to each other, and therefor have no legal standing. They never 'marry' because it would affect their benefits.
The people (friends) you refer to are obviously the old-fashioned kind who take their role seriously, and actually marry.