martinibuster - 3:32 am on Apr 10, 2008 (gmt 0)

>>>I have just been analysing 4+ years of AdSense metrics...

Now scrutinize 4+ years of log file metrics.

>>>Why is it that some sites seem to have increasing traffic AND earnings without any reduction in CTR?

I think that's the rare exception. Just my opinion, but from watching the ups and downs of my various niches, and the niches of friends and colleagues, it's far common to have wild up and down swings than to have a flat or happily increasing earnings trend.

>>>In which niches are these seemingly "immune" sites?

I doubt there are immune niches.

Judging from this thread it looks like you're having a normal everyday 33% dip, and it's not a systemwide glitch.