Strange unit of measurement. Who would find that more useful than expected compute or even just the number of chips.
I imagine this as a subtractive process starting with the maximum energy window.
Because if some card with more FLOPS comes available, and the market will buy all your FLOPS regardless, you just swap it in at constant y / for no appreciable change in how much you're spending to operate.
(I have no idea if y is actually much larger than x)
Therefore, they are listing in terms of the critical limit: power.
Personally, I expect this to blow up first in the faces of normal people who find they can no longer keep their phones charged or their apartments lit at night, and only then will the current AI investment bubble pop.