Yes, there is a difference. Coke is a cola. Pepsi is a cola. Coke and Pespi do not taste alike; most people drink one and not the other, and the people who do drink them indiscriminately are usually waiting for what they really want, alcohol.
When I read on-line pablum about, "I just enjoy whatever, and shouldn't we all just read good stories wherever they are written, and I don't think there is a difference, and I want to read a cross-over where Iron Man dates Power Girl, and why can't we just all get along?," I want to take an uzi into a bar and slay a score of second-rate villains in a hail of bullets. But I don't. Why? Because that's a Marvel thing to do, and I'm a DC person. It says so in the blog title.
One of the examples of the Difference Between DC and Marvel is in their panthea (or pantheons, if you're allergic to Greek plurals).
The Greek Gods, the gods of tragedy, are the gods of the DCU.
The Norse Gods, the gods of opera, are the gods of the Marvel.
We see lots of gods and godlings in the DCU: fun, forgotten ones in Vertigo, ham-handed manques like the New Gods, decorative dieties like Rao tossed about the universe like theurgic throw-pillows to spice up alien cultures. But for the most part, the "gods" in the DCU means Zeus & Co. Yes, the Greek Gods, the gods of founders of Western Civilization, the people who brought you self-government, logic, and couple other useful concepts, like: tragedy. Now, not every DC story is a tragedy, of course. But if you set aside the "gosh, that's sad and icky" part of tragedy, its underlying tenet is that what happens to you, your fate, is the usually the result of your own character, not just random happenstance.
Batman's "fate" isn't thrust upon him by a cruel world that fails to understand him. Bruce Wayne could, at any point say, "Well, this is fruitless! Alfred, pack my bags, buy a Caribbean island (if I don't already own one), and tell Silver St. Cloud I'll meet her there for brunch!" But he doesn't, because his character is otherwise.
Superman isn't enfeebled by the mistrust of a xenophobic society, forcing him to hide as a mild-mannered drudge. "Gosh," Superman could say, "I think I'll rule the world today, then write about it in my gigantic steel diary using my fingernails." Because of his character, Superman chooses (like Cinncinnatus) to rise up above other people only when it is necessary to protect society; otherwise, he chooses to live among them as equals. Whatever "tragic fate" these and other characters suffer stems from their own virtues and flaws (which usually aren't fatal, unless you were a member of Justice League International, like Ted, Tora, those foxy French sisters, and Amazingly-Brittle Man).
But Marvel's gods are the Norse ones, who, in our culture, we know mostly through opera. It's fitting; Marvel is about personal drama, people thrust into extraordinarily roles and situations (usually against their will) by life's vicissitudes (you know, errant chromosomes, cosmic rays, radioactive spiders, and such). It's opera, not tragedy, because you are watching people suffer unjustly, to see how they stand up to it all (like on Fear Factor).
DC's message? You are responsible for protecting and improving yourself and society, so toughen up for that responsiblity.
Marvel's message? You better be tough, because you're going to have to suffer many things in this world that you're not responsible for and can't improve.
Both messages are completely true, of course, which is why each company does speak effectively to so many people. But, in my eyes, DC's message is designed to inspire and Marvel's message is designed to console.
And I know which I prefer.