I agree with Houde's agreeal of E.
Here's another semi-related thought to ponder on: Back in the day when comics cost less, crossovers were semi-justifiable because it was actually possible to buy most of an imprint on a monthly income. I remember reading somewhere in a book I have, "Comics and Ideology," that it was financially realistic for 'Marvel Zombies' (no not those zombies) to purchase the shared universe on a monthly income, but greed drove Perelman, et al to expand the line and jack up the prices to where we are today, in which people (myself included) whine constantly about how sprawling crossovers are just murder on the wallet.
Of course, as E pointed out, comics aren't a necessity, and no one is putting agun to our heads to buy all the other books. But the point is that had prices remained stable from 1991 onwards, it would have been possible to collect the whole of Civil War on a monthly income.
My point is that it makes more sense to make an entire shared universe financially accessible so that you have an audience where everybody buys all in... and then grow that audience through word of mouth so that you have a legion of shared universe drug addicts paying Marvel and comics retailers a stable sum a month... than it does to increase prices and make the purchasing patterns more unstable and unpredictable.
As it is, even the most financially conscientious people have to groan and think about which books they will or won't purchase and drives them into a neurotic state. Do I buy ALL the books for Skrull Invasion, or just SOME of them... and if so, which ones? The ones that involve the characters I'm most interested in or the ones that matter most to the story? How do you define what matters or not? Does Newsarama have the right say on that? Or is it the people on Millarworld?