No one's saying "let's do stuff the stupid way!" - they're saying hey, let's focus on getting users before fleshing out the technical details of the what-if-we-actually-make-it scenario. Or, as the classic saying puts it, don't put the cart before the horse.
Unless you are building a technical work of art, it's all about finding the right product.
Ex: If your building a game with N players that can see each other walking around then that's N^2 updates.
Now, plenty of ways of dealing with that problem, but it's something to keep in mind even if you solution is not yet worth implementing.
Most likely you'll never reach Google scale, but, you'll be happy you did that as the application grows more complex and you don't have to test every part of it for each tiny change.
It's a good way to build non-scalable applications. Because if you scale the application, then at some point, the computer's time will become more expensive than developer's time. Of course, that cost is economic externality for the development shop, so why should they care?
Edit: I am not sure word "scale" is obvious. There is Google-like scaling, which is we run the software on many machines in house. But there is also Microsoft-like scaling, which is many users run the software. Collectively, they have pay the cost and they have to waste the energy.