The vocals in the Chicago set are in the mains. The vocals in the Talking Heads set are mostly in the center. Completely different channels. My Elton John and Steely Dan discs have perfectly balanced multichannel. A 7 out of 10 isn't a bad score. That is above average. Some of the discs in this set individually might rate higher, and some lower. But 7 is an average. Not everything rates a 10. Perfection isn't typical and typical isn't perfect.
The Rears are in the Rears in both cases, regardless of whether the vocals are coming out of the Centre or the Front L&R.
Hence, as I already mentioned, my feelings you may have some as yet undiagnosed front to back setup issue there.
Meantime, I can assure you I've been voting in these QQ Polls for a while now and I try to consider all aspects of these discs carefully before I vote. Also, I do my best to ensure my surround setup is correct before voting.
In an instance where I suspect (but don't know for sure) that there may be some issue, I ordinarily hold off voting until such time as I can establish what's going on.
Meantime, I accept what you're saying re: not everything's a 10, it's an imperfect world and all that.. but when a new member such as yourself comes along and starts voting things down on the basis they have weak vocals up front and overpowering rears, well to me it looks like something might possibly be amiss with their rig.
I'm only trying to help out, you can choose to ignore the well-meaning advice of others here of course and blame the discs for being poorly mixed, it's up to you.
back in the day, I held the little white chunk it in awe...and then my wife said something like "Ooh, cool...and videos, too?" Well, we spent a few evenings enjoying the hell out of it. What I also dug was that the limitations were explained in detail, for better and worse. And it's still the one box that that I like just for its unique yet ergonomic design. It would be a showcase piece, except every so often, I'll pull one out and just let it rip. 
