Walking up to 4 miles per day on asphalt, day after day, sounds like the problem. If he were my dog, I would rest him two or three days, then walk him on a dirt surface and see if the problem goes away.
Update on all of this:
In spite of my repeated inspections I could not find any indication of any damage anywhere on his two paws.
I did exactly what Sage said here and gave it a 3 day rest - then the first night we were out, half way around the 1.3 mile loop, IT POURED RAIN on us to the point where both my blackberry and 30gig ipod completely shut down.
We got home, dried off and went to bed. When I woke up, two of his pads were completely dangling from his paws - something Ive never seen before. Seems like the soaking did something to detach some damage that was occurring but was not at all visible to me.
Well, we took several more days off and have been very slowly working back up to the ultimate goal of at least 4 miles a day. There has been no paw licking or any limping and I still check every day to see if there is any damage.
so - for anyone who does a search and comes across this thread:
Asphalt seems to create damage that is VERY hard to detect - even in the dark or at morning or evening hours where heat cannot possibly be a factor.
Additionally, I walk bare-footed with him the whole way (always hated shoes my whole life) so even this is no window on what is possible damage wise with them.
My end analysis is that there was uniform damage going on to the entire pad and because it was so uniform and gradual, it was not visible...until a massive amount of moisture was mixed in and caused the ENTIRE pad to begin to separate, uniformly.
I hope this makes sense to any one in need in the future because like I said, it was just not visible in any way on account of the uniformity of damage - non-localized in any way and to me, completely invisible.
Thanks for the input and help. I hope this will help someone else in the future.