Adwords keyword tool - what happened?

For doing my research into optimal keywords to create pages based around, I've been using the legacy Adwords keyword tool as opposed to the new one. I prefer its layout and ease of use; however now Google seems to have axed it and is forcing the use of the "new" version of the keyword tool.

Upon using the new KW tool properly for the first time, I noticed something strange... the global monthly search estimates using the new tool for "exact match" on keyword phrases is significantly lower than before. For example, in the old keyword tool, [diamond] got 823,000 "exact match" searches per month; in the new tool it says 135,000. This phenomenon seems widespread and not just confined to a few keywords - and the words I am examining are not particularly "trending" terms.

Any ideas on why this might be? How can their search traffic estimates be so widely different? I can hardly imagine that google gets 1/5 of the traffic it did a year ago. I've tried mucking around with the "advanced options" parameters to see if I can get the data to resemble what went before, but no joy. Am I missing something?