I spoke too soon.

AND I figured out another piece to the puzzle.
It's not wireless vs wired. It is static vs dynamic/dhcp.
For example, with one of the laptops that I was testing with, I had the wired connection set to static IP and the wireless as dynamic. Plugged in...it was accessible to the other wired (static) devices.
But, when plugged in and set to dynamic.....nadda!
Any ideas on the static / dynamic isolation now? :0