That's exactly it to my mind.I am under the impression that an AVR is also an amp. Or am I wrong.
An AVR is limited by it's budget, as are most components. With an AVR, companies have to cram in more features, hence they compromise on the quality of their components vis-a-vis their lesser featured counterparts which can focus only on the stereo aspect of it. The Marantz SR7010 that you have is a pretty good AVR and I'm sure it has excellent sound quality. It's a good deal more expensive than the 8006 and therefore, ideally ought to have a good deal allocated towards its amplification.
There's really no rocket science to it, especially to warrant the surprisingly strong reactions.
In fact, i consider it mind boggling that the Marantz NR1509 which i got for some 27K does what it does and still sounds great.
Does it have the same level of performance as my stereo? Objectively, Absolutely not. But it's good enough for most intents and purposes and has enthralled many a person till date who've not come with their critical thinking caps on. For quite a few of them, it's the best system they've ever heard (due credit must also be given to the Mission QX-2).