Comic books aren't competing with other comics or being damaged by piracy so much as they're competing with video games, movies, music, and more. They aren't competing with baseball cards or riding around on a dirt bike any more. Is the latest issue of Daredevil more entertaining than Saints Row the Third? In a way, that's comparing apples to oranges. But to consumers, they're both entertainment options.
I suspect this argument cuts in all directions. The range, breadth, and availability of entertainment has broadened to such a degree that competition between all flavors of entertainment has also increased. I'm becoming convinced it's a cycle, and not simply a one-way street.
Here's an extended example. A friend of mine who's an avid gamer has described his preference for video games in terms of cost-effectiveness. If you spend $50 on a game that gives you a few hundred hours of gameplay, as opposed to $25 for a newly-released movie that you're going to watch only a couple of times (if even that), which of those is the more sensible investment? Ditto a newly-released $25 hardback, or a $15 trade paperback, or what have you.
This isn't to say that it's not worth spending $25 on a movie. I know I would gladly blow $25 on some movies without blinking. It's just that such decisions exist in far less of a vacuum than they ever did. Once upon a time, the only way to spend that much money on a movie was to take a ton of people to the theater or to buy a ridiculous amount of popcorn and soda. Now you can blow that kind of money on a film without even buying the refreshments, so of course spending $50 for something that will pay you back with far more entertainment over time will seem that much more appealing.
Likewise, video games are themselves being eroded — sometimes from within, as per casual games like Angry Birds, and sometimes from without. I strongly suspect you will not be able to find a single niche of the entertainment world that has not discovered it is losing its core audience in some form to ... other niches of the entertainment world.
A parallel phenomenon appeared in the tech world with the rise of tablets. It wasn't that people would stop buying PCs or notebooks altogether and start buying iPads or 'Droid slates — it was that those new devices opened up a whole new market for people who didn't really need a whole PC. I personally do need a full-blown PC; the range and type of things I do on a computer simply isn't supported by a tablet. But I can't begrudge anyone else their choices — and I can't deny that the appearance of those devices has given us that much more granularity of choice.
That's what it comes down to more than anything else, I think: increased granularity of choice. There's more games in town than ever, more ways to spend an (increasingly-scarce) entertainment dollar than ever, and we ignore that at our own peril. It's why it makes that much more sense, as much as I hate it, for a given "entertainment property" to span multiple incarnations. To make a movie, video game, novelization, comic, etc., etc. from the same thing is less a form of mean-spirited artistic invalidation — as some people might have it, me included once upon a time — than it is a kind of fail-safe redundancy.