Symbian S60 and Symbian 3rd gen is the same (or actually 3rd gen is subset of S60); Maemo and MeeGo is the same. That makes it down to two platfoms.
They actually have also S40, but that is for feature phones. I believe that they want to get rid of S40, put S60 on low end and MeeGo on high end phones.
OK, I've got my facts backwards... Good for them on Maemo/MeeGo, I though they'd completely lost it there.
But Symbian 3rd gen (aka. Symbian^3) is indeed different from S60 (which has 4 editions: 1, 2, 3 and 5), with 5th edition becoming Symbian^1. As a matter of fact, Symbian^4 (in which the current UI is replaced by the Nokia Qt SDK) is positioned for a 2011 launch according to http://en.wikipedia.org/wiki/Symbian_platform
It's the Qt SDK that I counted as a new platform in itself.
Long story short: Focus. Nokia can't have two promising and incompatible smartphone platforms.
Yes, I agree with you, they lost focus wrt their platforms. The first step for them is decide, what they want and then follow with steps to achieve that. And only that, no forking and dead ends.
They actually have also S40, but that is for feature phones. I believe that they want to get rid of S40, put S60 on low end and MeeGo on high end phones.