Sounds like your parents made a wise decision when it comes to the money, but let's be honest here and call it like it is. Many of these people are taking out these loans for materialistic things such as cars, maybe they want to expand on the home to "add" more value to a perfectly stable home. Basically focusing on wants instead of needs.
As far as Renting vs Owning:
The Tri-State area is a whole different animal all together. A big down payment up there is damn near mandatory to get anything decent and not have a ridiculous mortgage, but at least there is an end in sight. I will give you my example...my mom has paid on average about $1,400 a month for an apartment in Manhattan for 26 years. Dog thats close to half a million dollars gone already...she can give a 30 day notice tomorrow and will have ZERO in return. At the very least it would have been a place PAID for me or my sister OR use that capital to invest or look for a cheaper place elsewhere and pocket a cool 200-300K. That's her position right now as she is thinking of moving and owning now.
I understand your argument about oil costs and the potential to LOSE some value in these rocky times, but getting SOMETHING in return is always better than NOTHING. The prices to rent anything decent in the city is about $1,200+...I can't live with myself thinking that I am forking over $1,200 a month and not even have the opportunity to watch it grow in any way...and if I DO lose some of it at least its not a clean $1,200 GONE. There are some parts of Massachusetts and New Hampshire in where the houses are dirt cheap and when compared to the rentals in the area its basically a wash...maybe paying a bit extra but the advantage of owning outweigh it.
My girl and I are in a rent controlled apartment, her Uncle's friend owns the building so we pay comparatively nothing to be honest so there's very little incentive for us to buy a house. If we didn't have this, we'd be living somewhere in CT, probably New Haven since you can get a multi bedroom apartment there for 500-600 a month

And that's the underlying issue, houses are cheap in areas not many people want to live. Me, I don't really care all that much but if I'm going to move to a place where I don't know anyone it's going to be a warm weather climate.