"Canon wasn't even kind enough to keep backward compatible TTL light communication so you could keep using all of your now obsolete and soooo 2010 pre-600 series flashes."
Nobody cares if you are a stick in the mud, or if you can't realise the value of a manufacturer supplied option, to you it might not be high, to others it is good value. When compared to a 580 EX II and a PW the 600 is a bargain.
But where on earth did you come out with that rubbish? The 600 is 100% compatible with all previous optical ETTL flashes.
Well, I'm not sure how illustrating the obvious on my comments about myself and value perception is productive but whatever.
As for the backward compatibility, that actually isn't rubbish. I just neglected to be more specific because something came up and I had to run. (I'll edit the post right away.) The ST-E3-RT controller
(which was my mental focus at the time) is NOT backward compatible with optical and WON'T control anything but the 600EX-RT. The 600EX-RT as a master is supposed to control everything according to specs but I've read in some places where folks have had some issues or group/zone limits or something with the older flash models mixed in with 600 units used as optical slaves. Since I don't own a 600, I can't really speak to that, that's just hearsay. At any rate, it does sound realistic that if one wants the 600 series stuff to work best, one should not try to mix old and new and that seems to be a pretty common opinion. So backward compatibility is probably a moot point anyway and that's too bad.
So with that said, I would expect upgrading to a 600 series only flash system to be quite expensive. Well over $1000 at least for just two units and nothing else. Everyone has their own priorities and budgets. As I said before, not a big deal and it's all good for them if that's their choice. Just not good for me. I don't think I ever said others wouldn't benefit. But if one already owns 580 units and some kind of satisfactory RT solution, PW, RP, YN or whatever works, I don't see much value in replacing it all with a minor upgrade such as the 600 series. It's just not that much of an improvement in that scenario, which happens to be my situation and likely many others'.