Some review sites are known for using old benchmarks for comparison because they can't find the time to re benchmark again or because they're lazy. Rx470 and 480 have gained performance since their launch and need to re tested for a fair comparison with 570 and 580 cards.
And this is one of the major reasons why rebrands happen. If a card comes out weak (like Hawaii and Polaris 10) and later sees substantial improvements, whether in drivers or in better yields/binning, then most review sites will keep re-using the old results from their database, so the manufacturer gets no credit for the improvements. The only way to drive the old results off the charts is to rebrand.