How can you compare Doan's elbow to Keith's? You can't; it's irrelevant.
Keith's elbow was with a purpose, he specifically targeted Sedin. While I don't blame him, they are two completely different situations. Keith received the extra two games over Doan because there was purpose behind it, the problem is with the NHL covering up Sedin's hit by claiming that it was shoulder to shoulder.
The only question that comes into play is that Doan has a history while Keith does not, but regardless the two hits are not comparable. Although, with the fact that Doan does have a history of suspensions, that is just further proof that the NHL doesn't really have a bar set on what qualifies a short suspension versus a longer one and that prior suspensions don't really have any benchmark for future suspensions.