Do blogs degrade?

I subscribe to a large number of blogs. You can see them over on the side of this blog's home page. Usually I subscribe to a blog when I have read some (more than one) interesting, amusing, useful, or inspiring posts there. Few are consistently good. In fact, when I scroll through my blogroll, I frequently hit just a few of my favorites and just mark the rest as "read." If I do read the non-favorites, I often think to myself, "Well, that's more of the same from so-and-so." I have grown accustomed to, and therefore bored by, that person's way of expression.

So my question is, are the blogs themselves getting worse over time or am I just becoming over-familiar with certain bloggers' styles? I have noticed a similar phenomenon with newspaper comics. Only a few stay good for years and years.