Perhaps it's my head size and specific glasses, plus ears of course.Well, that's certainly a bit strange, the idea that the sound of the 560s is affected by glasses while the 800s isn't. I wear glasses, and I notice NO difference in the bass-response (which is what would be affected by seal loss) with or without glasses. And measurements support this: Solderdude at DIY Audio Heaven measures the frequency-responses of headphones with or without a seal-breach (including that caused specifically by glasses). He found only the most tiny, negligible change (about 1dB in the deepest sub-bass) in the FR of the HD560s with a seal-breach by glasses, and a MUCH BIGGER change in the bass of the HD800s with glasses/seal-breach. The measurements from rtings.com also support this, as they found up to 3dB to 4dB variation in bass-response from the 800s depending on seating/seal on the head, while they found NO variation in the bass-response of the HD560s (although they did find SIGNIFICANT treble-variation from the 560s depending on seating-position and almost no treble-variation from the 800s, but that has to do with how the drivers are positioned relative to the ears rather than with seal).
I do believe, from having listened to various cans at audio-meets and at local audio stores, that the HD800s are far from the best dynamic-driver headphones available in their price-range at this point in time, except perhaps when it comes to soundstage. Personally, I'd rather get a pair of Focal Clears if I had that kind of budget (HA, I WISH), or just ditch dynamic-driver tech entirely and get some planars or electrostats.
Something that won't show up on those measurements but they are welcome to look at their graphs and I'll listen to music with my ears!