I don't claim to have my finger on the pulse of mainstream music, but one thing that has jumped out at me over the past year or so, is the consistency and familiarity of the artists that get radio time. In the 80s and 90s (mainly the 90s, I was too young for the 80s) I remember a new "hot" band every month or week, with the following week having them fade into obscurity to be replaced by the new band of the week.
But if you look at the current top 40 singles and albums you see a lot of names that have been around for 5 years or so. They may not have always been chart toppers but people like Missy Elliot and Nickelback have been around for quite a while now, and really don't seem to be going anywhere anytime soon.
Again, I mentioned before I'm not too up on the mainstream scene so maybe I'm totally off on these observations, I'd be interested to see if other people have noticed the same thing, or think I'm totally crazy.