UPDATE: yes, but not trusting my eyes I re-ran it and then I tried some of the laptops and then I realized that I needed to be REALLY PATIENT when you see DisklessSetup.sh to let it build the MD the first time the laptop booted, now the laptops seem to work as MDs (but on AV setup I needed to set the UI to lightweight).
Encouraged, I decided that there must be something on the Media-Center PC that was preventing the boot from LAN even though it was first priority and I disabled every other device. Lo and behold, eeep inside a sub-menu in a part of the BIOS I'd never seen on any other machine there was a setting to enable ROM for LAN boot.
CONCLUSION: all devices now seem to happily boot as diskless MDs so only mildly curious about disked MD booting, as it looks like boot time wouldn't be a huge difference between disked or diskless.
Thanks for the suggestion,
A Happy LMCEer