two vastly different charts showing user base vs 'Droid version

I'm curious about something. Just a week or two ago, I saw a charge (didn't check the age on it) that indicated that Android versions 1.5 and 1.6 each accounted for about 1/3 of the total user base. Just a little while ago, on the
developers forum, I saw one that showed Android version 2.2 being the vast majority, by far (looked like about
90%). So I'm curious. Was the first map just really old? Or was there just recently a MAJOR series of upgrades
to older phones?

Later,
--jim