Amazon's listings can be a bit tricky to understand sometimes, so here are a few tips:
1) The percent off listing is likely based on Amazon's list price and the lowest listed price Amazon has access to. This includes individual stores. I got a sneaking suspicion that other discounts like super saving shipping is taken into account too, but I haven't been able to confirm it. Some stores manipulate their prices to show on this list, which might skew the results.
2) Justin Vaughn notes that Amazon has had a tendency to overprice the base price in the past. I have only noticed this on outlet items that aren't in production anymore, but it's always wise to check other sources before you buy.