I've been playing a ranged DPS class as my main for almost 7 years now, through various MMO's. I always knew to wait a few seconds to let a tank (especially a new tank or someone I didn't know) get aggro before opening up on a mob/pack of mobs/boss. In most of those games, if I pulled aggro and a mob ran over to me I could probably tank it for a few seconds and let the tank grab aggro again. If it was a raid boss, I was probably instantly dead if I didn't have a cooldown up.
Trust me when I tell you that when endgame comes, DPS is going to chill out and let you get aggro because the last thing they want is a pack of elite mobs or a boss walking over to them and pwning them because they blew their load 3 seconds into the fight.
I leveled to 40 as immortal spec with a few points in vengeance to upgrade my Smash ability. I rarely had a problem keeping aggro but when I did, AoE taunt, single target taunt, force choke/grip, force push, and force charge ALL helped me get aggro back or divert aggro from someone else taking damage. I realize that all of these abilities are much harder to coordinate than a Bounty Hunter rushing in a blowing everything up to keep aggro, but the fact remains that we have them available to us. Not to mention that the classes in this game can all take a spare amount of damage in comparison to most traditional MMO's. It's probably ok to let that non elite mob get owned by the folks in your party while you tank the big mean guys.
I honestly believe that an adjustment to the amount of PvE threat generated in Soresu form -OR- to our AoE abilities - would probably help ensure we keep aggro all of the time.