Doing pushups involves your slow twitch muscle fibers, as does benching. When your pushing, your using your triceps, your shoulders, your back and your chest, as with benching. its the same movement, only body weight, not free weight. i know for a fact it helped my strength, the reason i went from 335 to 345 was pushups alone. Now i'm 6'4 and 260 lbs, so my body weight is ultimately greater than yours (im assuming) so it would affect me in a different way then you.
How does it help mass? Have you ever seen a wrestler? im talking real wrestling, not pro wrestling. 90% of what they do is ALL body weight exercise and look how ripped up they are.
And how doesn't endurance help your bench? i'll give an easy example, if your maxing out on bench and say your on a third attempt of 325. You rest for 5 minutes, your muscles will recover faster, or atleast be used to the amount of strain your going to put on them, so you'll have a better shot at pushing up the weight than you would if you hadn't done some kind of endurance exercise.
