DC was on his way out. But the major point behind it was that DC was brought in to help test and develop the Jaguar into a decent car and was considered one of the best feedback drivers along with being very competitive in races. Redbull was having issues bringing up their STR drivers as most of them sucked. With an open seat and knowing that DC was on his way out they brought in Webber. But it was 3 years after Jaguar and 2 years after bringing in Newey.Well, I think when DC was replaced by Vettel, Webber took over that role.
Also, Webber said, he will retain his ties with RB, after leaving the F1 Team.
More hints at a possible RedBull-Porsche Team Manthey for 2k14 at LM?
Now Webber is redundant. They have a probable 4 time Champion and now old hand. They can keep bringing in new young guys as much as they want now. I do agree that Webber is a better image fit than Coulthard (though David did try to live up the Bachelor life as much as possible with them).