I don't like this new startup trend[1][2], nor do I think it actually works.
Literally all of those examples are the opposite of what the blog post is claiming. They did have a product: Hotmail had the service built out, Eventbrite had the service built out, and there was a Dropbox before you could refer your friends to it. There are examples of what the author is claiming, but most are gimmicky Kickstarter-style (and often derivative) products.
I mean, think about Dropbox or Slack or Instagram: how could you possibly sell (or even validate the idea of) those products without actually giving some sort of demo? Without people actually using that thing? It might work for something like the product in the post (people understand what "video chat" is), but I don't really see it working for any kind of particularly novel or value-generating product.
Followup: grabbed a coffee, and this post got a bit of attention. To be clear, I think that an MVP should be just that: a minimum viable product. By definition, you shouldn't be able to go leaner. I also think that sometimes people conflate "fake it 'til you make it" with PG's "do things that don't scale" -- these two are not the same.
[1] https://tommorkes.com/lean-launch-how-to-sell-an-idea-before...
[2] https://hbr.org/2013/12/sell-your-product-before-it-exists