I realize after reading a few comics and myself over my lifetime that I notcied a few difference as well as similarites in the story aspect of comics or manga. This isn't a manga versus comics thread as I had lurked in those threads in other forums and while some can be pretty thought provoking, sometimes I find I find endless trolling and nonsense. I do not have or know all the differences but I had noted some matters such as:

1 For one thing in terms of storytelling, manga tends to be a little fast paced and they tend to spread onto more issues before a story arc is resolved. Western Comics save graphic novels tend to be self contained stories that pretty much focus on story and character development.

2. Both mediums have many different genres that many writers and artists explore but I find that most of the time, the consequences of the protagonists are somewhat more explored in comics than in manga where thet are pretty much excused of their actions in the story.

3. On the storytelling aspect, I notice that comics have a smaller story arcs that encompass a longer, complex arc but manga specifically ongoing manga tend to go on one arc with one antagonist causing all sorts of trouble in an arc until the next one shows and is apparently more powerful than last antagonist who had somehow been deposed of.

4. Japanese manga tend to be a bit more visual with its storytelling than Western comics that use mostly dialogue.

I am only making generalizations, I hadn't read that many manga or comics but I had noted some differences in storytelling as well as the art. Again, I do not know too much on the subject and I might as well be horribly worng on the topics at hand but these are my thoughts on the subject and this is not a comics vs. manga thread, I enjoy both mediums.