The 320 just designates engine size. i.e. 3.2L V6
The new 350s, are still the E class, just with a 3.5 V6
But it's not. There was a redesign between those model years. Mercedes rarely updates engines mid-cycle. In this case, it was a dramatic redesign, an entirely new platform. The new E Class -- E350 or E550 -- is a very different car than the E320.
And in the case of the E-Class, 2009 was the last year of the old generation (W211 IIRC). So yes, if you graph E-Class prices right now, there will be a huge drop there.
If the 2010 Data Point is something he's purporting to be a "2010 E320" then it must not be a US model. In the US MY2010 began the W212 E-Class.
I applaud this guy for putting together so much data. I just wanted to raise this question because the way the data is presented confuses me a bit.