Doesn't this all depend on your assumptions, risk tolerance, and of course the math?
If you think that if your invested money will grow at 8% in stock index funds and you don't want to pull it out for a down payment (and pay capital gains tax) when someone is offering you 4% interest so you can finance 90%+ without PMI... well, it could be attractive to some people who don't mind the risk. If your assumptions turned out to be true you'd come out on top. But, the question is just how expensive the financed money above 80% is.
It's not like you'd foreclose if you lost your job when you have the money to buy the house in cash.
The other extreme: don't even finance it at all, but pull the full price of the home out of your investments and pay a huge amount of capital gains tax. I think most would agree that isn't a good idea unless maybe you're very wealthy. The opportunity cost is enormous. In between you could put anywhere from 20% to 100% down if you have the money. 80% is just the cutoff point to avoid PMI.