To add to your point about flexibility: I am vastly more flexible now than before I started lifting, for the simple reason that there's just no way I'd be able to execute even "simple" lift like the standard powerlifting lifts (that's bench, squats and deadlifts for the non-lifters) without hurting myself without being reasonably flexible.
To extent you get improved flexibility from lifting with proper form, but if you don't get flexible enough, you've got no choice than to work on it in other ways: Staying inflexible while lifting is a surefire way of getting hurt badly.
Body builders can "get away" with less flexibility, but as your pic shows they certainly don't have to be less flexible.
First off: even some really big guys can be amazingly flexible: http://1.bp.blogspot.com/-mO3twKxKpqc/UfaQxvShokI/AAAAAAAAV0...
It's really got more to do with tendon and ligament mobility than anything else.
The other: you're simply not going to get that big without drugs. A really good natural bodybuilder will look more like this:
http://mybodyhealth.net/wp-content/uploads/2013/01/tumblr_md...
That's defined, but not huge. And he's doing better than most.
You can get the positive results of strength training at or below these levels.