I, too, find this practice deceptive. For a random Seattle 4* I just pulled up, Hotwire states the following under "Hotel Details":
$119 per room per night
Retail: $209.00
You save: $90.00
Next to this, there is a big yellow star that indicates "43% savings" -- and if you click on that star, you see the following:
You'll pay $119 per night for this room -- 43% less than the retail rate of $209.00.
There is no disclaimer that this statement refers to overall, year-round, average 4* prices, and I would say that a reasonable customer should be able to expect that such a detailed statement refers to actual savings. Hotwire might be well-advised to adopt more general language ("Hotwire customers save an average of 43% on Seattle hotels," "Hotwire hotel prices in 2007 were 43% lower than the average Seattle 4*," etc.)