Rizyx: There had to be a - pardon, but I may have the dimensions wrong on the physical calendars it's been a while since I read-up on the Maya - but they first had to calculate all of the full, half, quarter (waxing and waning) and new moons for 5200 years, then add in the religiously significant dates which did not fall on one of those but were figured from one of them. This is way before anybody's astronomical tables and even more before anybody's algebra to calculate them. Many man-years of work went into figuring out what the calendar had to look like and there were relatively very few who were qualified to do the work. Then, each calendar was a stone wheel between 3 and 8 feet in diameter, with all that information on them as well as ritual prayers, illustrations of the gods etc all done by hand and without metal tools. Not a bronze age or iron age people, but neolithic - New Stone Age - people. Nothing wrong with that, just that is where they were at, technologically. Wheel sizes evidently varied based upon the political/religious significance of the town/city/temple where it was to be placed. This was a major task, not accomplished perhaps even in one lifetime, being handed on to the next generation of priests and artisans.
Furthermore, in order to believe that they stopped their calendar because the world would/will end on 12 December 2012 would require that the Maya knew this to be true and that in fact it is true. And, furthermore, that the secret of that knowledge - how to figure out when the world ends - was known to a neolithic people but was lost and not rediscovered in the roughly 1200 years since the fall of their civilization. Too many assumptions. Occam's Razor - principle of parsimony - tells us as thinkers that the simpliest hypothesis which explains all the known facts is most likely to be the correct one. Hence, it being simpler to hypothesize that they stopped and didn't re-start is because it was too costly to begin right away and that their civilization lost the technical ability to make more/continue with their calendar system before it was time to make new ones, than it is to hypothesize that they knew the world will end that date, but somehow that knowledge and how to figure that out was lost and not re-discovered since. Why? Because the second hypothesis requires - logically - even more assumptions regarding the existence of "lost secrets of the ancients" sort than does the first hypothesis. For support, I refer you to youtube, search for a song called "It Ain't Necessarily So" and give it a listen. The older versions are better. Consider who is likely to gain fame and money: an academic who claims superior knowledge we have lost for the Maya, or the one whose explanations are more prosaic, and ponder what effect that is likely to have on the content of academic publications. If you consider that to be very low probability, I point toward behavior of the Global Warming alarmists in their attempts to provide "scientific" support for their hypothesis of catastrophic GW caused by CO2. I offer no opinion on the issue, only ask you to look at how the academics have behaved in that debate as support for consideration of the distorting effect of notariety and funding on the content of supposedly "scientific" papers.
Sorry. It's much, much much more romantic, exciting, mysterious and interesting to hold to the second hypothesis than the first, but sad to say, most of the time the prosaic is the accurate hypothesis, not the exciting one.
Just to stay on topic, a little bit, I hope that the radiation release from the reactors in Japan is on the order of Three Mile Island rather than of Chernobyl. The news folks in the U.S. aren't talking about what levels of radiation are present, for whatever reason, but still one may hope that no more misery is inflicted on those folks in Japan than has already occurred.