Every few years or so they bigger companies will reboot their universes, so it isn't impossible to get into at a later date. Like DC relatively recently reboot their entire universe and released their "Nu52" universe, so the last two years or so worth of storylines has been independent from the last 50~60 years before it. Sometimes they do it to boost sales, and sometimes they do it because a particular plot point becomes harder to keep "realistic." Like Iron Man, his original story was that he was hurt during Vietnam, which is hard to make work when he's perpetually 30ish years old, so they moved the timeline to the Iraq war. Captain America is pretty much the only one that can keep his original Punch **** storyline since he was frozen in time. They just move how long he was frozen.
Marvel and DC are the two biggest companies, but there are dozens of smaller studios that release books that aren't as expansive. I don't follow Image books nearly as closely, but I'm relatively sure their books don't really crossover as much or at all. On the other hand, IDW recently did a massive event where the Ghostbusters, GI Joe, Star Trek, and Transformers all took on a zombie apocalypse. That was kind of surreal* ...
You can always check out torrent sites for chronology. I do that once in a while. I'm going through Incredible Hulk right now. I tend to download new issues and then go to Midtown Comics to buy whichever books I enjoyed reading. I get to support books I like that way, and still don't really get lost in various intermingling storylines.
Edited, Apr 10th 2013 12:56pm by lolgaxe