We also read the BOM perspective and value their assessments.  And we know they are just as passionate and committed to "getting it right" as we are.  However, because ENSO is a climate phenomenon based on multiple factors (variables like SST, winds, rain, pressure) and timescales, across a large expanse of the tropical Pacific, it is not easily boiled down to a single number and so divergences among various national agencies arise on occasion. This was touched on here:

http://www.climate.gov/news-features/blogs/enso/why-are-there-so-many-e…

The BOM recently issued an El Nino Watch because they saw some of the same factors as we did getting into place.  However, they have slightly different criteria and thresholds than ours.  

Finally, I should emphasize that this is not a clear-cut El Nino.  It is weak and borderline.  For this reason alone, I am not surprised different agencies would not all agree on its status.   For those with a strong stake, I would encourage reading all ENSO assessments, which each lay out their reasoning, and coming to their own conclusions.