I remember when I wondered the same thing, then discovered that I just needed to click the Steel Soldiers banner. I really thought I found out a big secret on my own.
The little thrills in life.
I think a lot of folks just do the home page posts scan. That's probably why certain topics stay hot for a while, then once they get pushed down past the bottom, they're forgotten sooner.
Hence, the "bumps."
Nature of the beast, I guess.
I know I'm often guilty of it, (favoring the home page posts).