EVERYTHING is genetics. if you don't have the genes to bench 500 pounds, you won't.
that said, people often attribute things to "poor genetics" that could really be solved otherwise. sure, not everyone will deadlift 600 their first attempt, but i'd hazard a guess that given enough time and work most people should be able to come close to that. you always see some guy who weighs 180 pounds with a soft belly saying he has "shitty genetics" only to find out he drinks four days a week and spends more on porno mags than protein powder.
i do NOT have good genetics. my first squat workout i did 95 pounds for a set of 20 and nearly died. it took almost a year before i could even DEADLIFT 225 (i distinctly remember being at the gym with a buddy and using straps to deadlift two plates a side on the short 25 pound bar and feeling like a badass). i started lifting when i was 17 and four years later i was proud of myself for doing a damn board press with 275.
now, two years after that, i can hit 350 with a pause on the bench, pull 520, squat four plates for reps, weighing LESS than i did when i got that shitty 275 board press. my genetics didn't change, i just got my head on straight, ate better, and stopped training like an idiot. that's the key. i could have easily stayed in my rut and figured i'd never be able to get any better, but i didn't and actually started improving.
genetics ARE the big things, but people have a WAY skewed impression of where their genetics will stop them.