People are already debating what in the comic is or isn't canon... I won't be surprised if it comes down to "So, this panel is canon, but the next one maybe isn't, and this panel is canon but the balloon in the left corner isn't."
Is the debate valid, though? I'm of the understanding that Joss himself established all of the comics' major plot points before assigning them to the writers for completion. Doesn't that make the comics Whedon canon by definition?