Following on the heels of 52, DC Comics will apparently be releasing Countdown, another finite weekly mini-series.
Now if only Viz could tap into DC's system, we'd be getting Shonen Jump on a weekly basis instead of a monthly (as it was originally in Japan and dictated by the format)...
Of course while Japan has been doing monthly comics ever since, there are three significant factors that hampers the US from replicating such a feat.
1) Japan has a well-oiled, efficient machine that's been in existence for the past few decades. While the US has done weekly comics before, it wasn't always sustainable (i.e. not meeting deadlines). And Japan's comic production process is completely different from America.
2) US comics are colored. Those in Japan are usually in black and white, with the occasional splash page that's in color. It's another step in the production process but when you're talking about a weekly comic, you honestly only have a few days to create the comic. (And we're not even counting the days allotted for actually printing the comic.)
3) Japan occupies a significantly smaller geographic area than the US. While this has no bearing on the actual production of comics (or it might if you're coordinating with authors and artists from various states), it does have a bearing on distribution. And it doesn't matter if you produce a comic in time if it doesn't get distributed in time -- it seems late to everyone else.