@groin: 42 hp is enough to make the difference between 1 shot and 2 shot on several bosses/enemies; more endurance increases the number of swings you can take and the number of rolls you can perform/amount of damage you can block; in general it's around a 20-25% increase in survivability. This becomes most obvious with Stray Demon, but there's a lot of other situations where it does quite a lot. There's actually quite a few enemies that will one shot a sorc but won't one shot a pyro; even more depending on the gear you're using. If you're using Ring of Favor the survivability is increased another 3-4% Even a 1% increase is significant in a tightly tuned game. Apart from MMOs this is quite apparent in most action games as well. For example: the weapons in NGS2 are all fairly comparable but using the ideal weapon in the best fashion will substantially increase your killing power and efficiency.
I mean, no one would ever use Ring of Favor (you know, the most popular ring in the game) on any character if 40-80 hp wasn't significant, no need to upgrade your gear incrementally at all either right, it's just a slight increase. I don't want to do more damage/take less damage, I am above RPG elements. /sarcasm