I'm not sure if this is true but apparently I've heard that if you collect some chests and then open it rather than opening it one by one as soon as you get it, there is a higher chance of receiving a pink. If this is true, this assumes that when a chest is obtained, what is actually inside it changes over time. I tried this when the level 21 cap update for the first time collected 8 silvers and for the first time ever I received two awesome pinks, (vorpal sword of tactics sold for 250k and mighty heartseekers of brutality sold for 640k). During the level 16 cap, I literally went through about 45 elites straight, dropped 1 frikin legendary item lol.

I'm not sure if this is mere coincidence or if this is actually the case.