Besides wondering what's going on here, this story is interesting from the angle of studying information creation and propagation. First of all, even the drastic decrease in probability is not too welcome by people who write about this, because it's boring, and so this is not reported quickly, while even a slight increase is of interest (anticipation of more to come).
Now why on Earth NASA suddenly kicked out 58 observation points (a third), and why there is still no commentary at all (it was quite a few hours) ? Fake, unreliable, statistically incorrect results ? Good results dropped by mistake ? (And I suppose one can produce at least a dozen juicy conspiracy theories out of this.)
UPDATE: The Wikipedia article now reports this, and explains that precovered data were used to obtain the corrected estimates. So asteroid-wise the story has probably lost the significance. The Wikipedia article notes that the choice of 118 observations remains unexplained (probably one of those statistical things, trust them or not).
UPDATE #2. Someone at Slashdot offers a reasonable explanation: "Now, because they have ruled out an impact in 2029, some of the observations actually don't contribute to determining whether an impact will occur on the other, later dates (2037, 2044, etc). There have been hundreds of observations but the only ones relevant to the current potential impacts are counted on that NASA page." (Also a virtually unlimited quantity of conspiracy theories in that Slashdot thread, of course :-) )