The other element is leverage. If you put 20% down (which is higher than average), you are levered 5:1. If all houses double in value, your equity goes up 5x. (Example: $100k down on a $500k house; price doubles to $1mil, your equity is now $600k; you can now easily afford 20% down on the higher price house, despite the fact that it is now $2,000k from $1,000k when you started the process.)
The way I’ve seen markets move is that certain price bands are more susceptible to fluctuations than others. For example, over the course of a 4 year period you might see the entry point for the market go from $400k to $500k, while the $500-$600k band sees a 30% increase, the $700-$800 band sees a 20% increase, and the $900-$1m sees a 10% increase.
So while the entire market is moving up, certain bands become more affordable if you can capitalize on a higher percentage band.