I think I see where the problem is. PL limited the bids they show so that a 'saving of 70%' is the maximum possible scenario.

Looking at their 'median retail price' for a 4* in Amsterdam city center, March 25-28, the price is $333. Multiply it by .3 and you get $99- this is the lowest figure Priceline would show on that list, while on BB someone won a hotel on these dates at $75, or 77% cheaper than the 'median market price'.

As you said, there are winning bids for this area at around $75, regardless of the 'median retail price' on that date. That brings us back to the old knowing, that the price hotels are willing to accept has very little do with the market average price. My own experience on this exact zone was $72/night earlier this year, so I do believe the reports are accurate.

Back to the question of when is this data useful, I think its useful in places where a large saving is not common (Barcelona, Paris, some small US cities) and places where there is very small/no data on at all (medium European cities and small US cities).