The extreme examples are just to illustrate the tradeoff. Some architectural decisions have to be made in advance, because they are hard to take back. In your

The extreme examples are just to illustrate the tradeoff. Some architectural decisions have to be made in advance, because they are hard to take back. In your example, size of the property (if any) on which your house is standing is such a decision. Good luck building a pool in a 4-bedroom apartment. (Interestingly, you said, "like pretty much everyone does" - isn't that actually a sounder advice than YAGNI?)