IMO, generally higher frequencies are not as compressed as much as lower ones, and as such if you view them on analyzers you see a lot more movement. If you have a multi-band comp plug, throw it on your mix buss and fire up a preset, it most cases the bands on the high end will be compressing less (fast attack/release/high threshold setting so it not clamping down on the signal, etc.)
Also, I think an "even" mix when viewed through an analyzer you will generally see a larger hump towards the low end and the it kinda flattens out as the frequencies go up...Sometimes you'll see a small rise towards the high end. I think that's the whole fletcher munson curve and idea at work, as low frequencies need a little more volume/energy to be perceived as loud as mids, highs mids, and low highs. Sometimes you'll see a small increase or shelf on the high highs to bring some air to the mix.
These are just my observations, I don't claim to be right or "schooled".
Also, if you are using an analyzer to take a look at some reference work, fire up something like Arch Enemy's Rise of the Tyrant as compared to one of Andy's mixes, and you can see a hyped high end starting around the high mids on the ROTT mix...I think that harsh high mid combined with hot mastering make for an unpleasant listening experience. One thing I've always REALLY admired about Andy's mixes is they are extremely pleasing to listen to and still retains full frequency punch and articulation...All without ear fatigue.
