I think one deep flaw in the rewards model is the lack of a long tail, meaning zero rewards for evergreen content. There are ways to overcome this but have not seen one implemented at a platform level - don't even ask at the blockchain level.
Thus, users want "high rewards" because the earning window is so brief.
Agree with you in that way, the 7 days window could be took off for we have the possibility to upvote in oldest posts.
Well, if ads will be widespread on Steemit, then that is one way to share the income wih the content creators :-)
At the moment, it needs a bit of a hack to upvote an old post: automatically generate a fresh comment that then gets upvoted. Works, but not yet popular.