Marvel has never rebooted their entire universe like DC does --wait for it-- every few years. However, that may soon change. Both Marvel and DC exist in a "Multiverse" or a setting with infinite, or at least multiple, parallel dimensions. This is for a very practical reason: it allows them the freedom to create new and experimental stories without worrying about massive continuity problems (which they still have to worry about).

Some times writers will pitch storylines that sound great, but don't go over well with audiences, which requires retconning the story. In other words, they have to go back and fix what went wrong with new information. The biggest example of this is probably Spider-man who revealed his secret identity to the world during the Civil War storyline, but then that was erased by a magical being who removed the memory of his true identity from everyone. The cost: his marriage with MJ. Doesn't make any sense, but that's what happened.

Some times new artists get on board and they have a different take on a popular character, like you mentioned. That's just the way it goes. You can't have the same artist drawing the same characters for 50 years. That's why costumes get slight or major alterations and characters are depicted with different spins.

Around the year 2000, Marvel wanted to launch new stories for old characters for a younger audience, so they created the Ultimate Universe where lots of characters were reintroduced with new origin stories, and sales were crazy. But of course, it got messed up and now they're folding ALL the Marvel Universes into one universe called BattleWorld. No one knows what universes will spin back out of Battleworld once it's all over, but it's their way of streamlining things.

DC, meanwhile, as I said, reboots every 10 years or so. They have for several decades. Every so often they introduce a major event like Infinite Crisis, or Crisis on Infinite Worlds, or FlashPoint Paradox, or ... you get the point. In the end they get to reboot some old stories. Meanwhile, Batman does that but also continues in his own weird timeline. It's very strange, and I don't understand it all, but a lot of it has to do with the different earths each story occurs on.

The best way to read comics, IMO, is to follow specific set stories done by a writer/artist team and when that story is over, pick something else up.