I do hate to be cynical, but I get the impression Boeing are releasing this more because they felt it was time they released a new plane, than because they actually had any worthwhile purpose.
And if Boeing didn't release a new airplane, you'd be slagging them off for not doing so. Based on recent sales, it appears to me that the 757/767 have reached their sell-by date -- Airbus A320 and A330 are outselling them. So isn't it time that Boeing replaced the 757/767 with something that is bigger/better/faster?