When I first saw a clip of Matt Smith's regeneration, I got the immediate sense that Moffat was having one of those fanboy debates with Davies about what really happens during regeneration, of the sort I remember from the heyday of RADW:

As I remember it, one school said that each version of the Doctor is actually a replacement of the one that came before -- a swap-out with a parallel universe, and that the previous Time Lord ceases to exist, on a fundamental level. This is clearly the school of thought RTD belongs to (Not only did he have Ten whining "I don't wanna go," he also had Nine tell Rose: "...it means I'm not going to see you again," instead of the other way around). Whereas Moffat belongs to the other school of thought: that regeneration is a natural, biological, process, only slightly different (although more complex) than the ordinary aging we humans experience.

And after seeing that fan made trailer, it became crystal clear to me that the main reason Clara's reaction to the Doctor's regen is so similar to Rose's in "The Christmas Invasion" (Even though it makes no sense, plotwise), is that it gives Moffat his one chance to rebut that whole whiny "What will I do? My Doctor's Gawwwn!" shpiel.

And since he has the Doctor say exactly what I wished he would have said to Rose in TCI, I'd forgive a plot hole the size of Belgium...