Great gallery, no doubt about the quality as it shines through. Very competant in all fields.
Congratulation on your Head Curator on 1x.com, obviously you have allot of time on your hands and dedicated to those Swedes.
To answer you question "500px do the best images really make it to the top or is it a popularity contest ?" The answer is very clear and easy as ALL internet photographic sharing sites are more or less the same, based on social interaction and popularity. If you have a very good reach on social media platforms - the more popular you will become is usually the case.