Considering how often Driscoll trolls for controversy and attention while pre-emptively (now) claiming to be taken out of context, Don Carson has been a little too nice in his response. Then again, I'm not hugely surprised Carson would decide to take the high road on this particular point, or perhaps I would say the polite road.
Then again there's a dynamic of popularity at work between Driscoll and the old men who back him. What he has to gain from being seen with old men with academic credentials he'll probably never have is saintliness and scholarliness by association. If he's seen talking with R. C. Sproul or J. I. Packer or Don Carson Driscoll looks like he's even more important in the global church than he's likely to be. What old guys get in exchange is to look hipper and more relevant even if they already really have nothing to gain in substance by hanging out with a guy who posted as William Wallace II and publicly wrote stuff like "This is all just gay". And to be fair I'm sure more than a few of them may sincerely hope that if they hang out with the guy often enough he may behave more maturely in public. Well, he might ... if he were actually like them.