One commenter online was mentioning that he thinks that the appeal of comic books is that the characters transcend time. The setting may update, but the characters are still around. If you kill off a character, you risk changing the environment of the comic too much. After all, the hero and his actions are a reflection of that. Superman does not handle problems the same way Batman does. Hell, even the Grey Hulk and the two Green Hulks handle problems differently.
But here's the thing -- where's the dividing line? Part of what makes such stories exciting is that the hero is in mortal danger. How's he gonna get out of his one? If your hero is never truly in danger, there's nothing interesting going on here, it's just a series of events to go through.
Complete changes can work. When Barry Allen died in Crisis On Infinite Earths, it hit me. He was a character I liked and admired, so his loss was hard. Wally West was a lousy Flash for a while. Then Mark Waid took over, and Wally came into his own. So much so for me that I refuse to deal with Barry Allen's return. Waid was also responsible for the relaunch of Legion Of Superheroes/Legionnaires after Zero Hour. He was on the title for a year, and had me hitting the comic shop on my way home as soon as the books came in to see what would happen next. He had stripped the Superboy connection, and the series worked great (my favorite issue was Brainiac 5 and Andromeda's discussion as he worked out a cure for her, backing her into a philosophical corner). His fingerprint was so indelible, that I left partway through the next major story arc. I felt the new writer just didn't get it. The stories were not only becoming less believable and more contrived, but the interpersonal relations suffered and (most importantly) the art was giving me a creepy vibe. Before, the uniforms were tight because they were superhero outfits and it was the future. Afterwards, they were tight because they were trying to make the characters sexy (THEY'RE UNDERAGE, GODDAMMIT!!!!). When I saw XS drawn with every muscle in her ass fully realized, like her outfit was literally painted on, I dropped the book cold.
A relaunch or a change can work when done right. Admittedly, doing so with the star of the book like Batman or The Flash is far more risky. Legion, for example, was an ensemble cast, and the focus could shift as needed. But it isn't done today because there is an interesting direction to go in. It's done to sell books. It's done to motivate characters that shouldn't need that motivation. For a long time, I commented that Barry Allen was the only comic character who stayed dead. He was treated as a true hero for giving his life, a consequence other heroes never had to face. Now, he's back, and the glowing admiration seems wasted.
It's not altering a series that is so cheap, it's doing it in such a generic way. If the readers aren't invested in the story, they aren't going to react, they'll just catalog the data, snark online, and that's it. They can explore new directions, but it has to be an exploration, not a cheap publicity grab.