Abs on a skinny guy are like boobs on a fat girl: they don't count.
I blame the media and magazines. I also think that when the general publich started to realise that the people like Arnie that they were idolising, were using assistance, they realised that their physiques were unattainable. Combine that with steroids being villified in the media and people need a new goal physique: along came the Abercrombie model with abs. Job done.