Street prices vary over time and location. For example, I have zero issues getting a 4090 at RRP where I am in Australia. Using RRP for comparisons makes the comparisons more universal and evergreen.

If you're considering a new GPU you'll need to know the state of your local market, so you can take the findings from Lambda, apply some knowledge about your local market (e.g. 4090s are actually 1.5x RRP right now where you are, or whatever), and then you can redraw your own conclusions. Alternatively, if they were using "street prices" I'd also have to know the state of their local market (wherever that happens to be) at the time of writing (whenever that happens to be), then work out the conversion from their market to mine.