Sorry for the thread drift, but I really want to respond to this as I just spent a bunch of time Googling PLBs and MLUs.
No an MLU is not the same as a PLB. The PLB communicates with a networks of satellites and will work anywhere in the world. An MLU sends out a terrestrial signal that can be picked up by an MLU receiver. Googling MLUs, I actually found a post here from PMR Iain describing the differences:
The rescue Iain is referring to in January 2003 I believe was a party of Mazamas who not only had a MLU, but had multiple cell phones and GPSes and were on the southside of the mtn where there is cell reception. If the Mazamas were on the northside, they probably wouldn't have been able to use their cell phones to request a rescue, so it would have taken longer before anyone went looking for their MLU signal:
http://www.pmru.org/pressroom/headlines/hoodstranded011203.html
Again, sorry for the thread drift. It was the Oregonian who brought the MLU subject up.