RE: clamshell mode...
Hi archdelux,
Clamshell mode is considered a feature by Apple...so if you want to sleep your AC powered and external monitored MBP, you either leave it open, click the Apple menu icon, and select Sleep, or you can close it, wait for the external monitor to reawaken, click the Apple menu icon, and select Sleep.
As you state, the nvram trick appears to work on only certain MBPs but not all. Perhaps someone else has found a final "fix"?
Switon