Originally Posted by
Mister Mets
These are posts on a message board, so people aren't going to go into that much depth.
Typically, the changes do have some kind of basis.
The Silver Age was largely an effort to tell inventive stories for all ages after Seduction of the Innocent.
There are some developments that have affected recent comics, including better printing quality (which allows for greater artistic detail), methods of allowing readers to catch up on earlier issues which allows for more complex stories, greater coloring, etc.
Peter David described that change in his book "Writing For Comics."
It was a rather significant development, and I would agree that it kicked off a distinct age.
It probably started roughly when Quesada became Editor in Chief of Marvel, when he had a line of cinematic comics, and there was the assumption that all stories would be collected in TPB format.