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The 20D did not have six assist points around cross type center point as the 5D/5D II has so 5D's obviously not simply the 20D focus
The 20D did not have the feature below (nor does any other Canon camera, except the 50D): From Canon 5D white paper:
Additionally, the center AF pointís f5.6-sensitive, horizontal line-sensitive sensors each have two lines with individual pixels arranged in a zigzag pattern, making a total of four lines for horizontal line-sensitive focusing at the center. With this improvement, the center AF point can now do a better job of detecting difficult-to-read, low contrast subjects, thus improving the overall performance of the auto-focusing system.
Some people have claimed that 5DII has a better center focus point than 7D. The description above explains why.
The 5DII also has a color temperature sensing capability, that no other camera before it had, in relation to pulsed AC light (i.e fluorescent lighting). The 20D did not have this color sensing capability.