Each of these applications is version specific. That is, they only work with the versions of the programs they came with. So, The CS5 Extension Manager only works with CS5 applications. Photoshop Elements, although it is not part of the Creative Suite, is released in relation to a specific version of the suite. Photoshop Elements 8 is tied to CS4. Photoshop Elements 9 to CS5. Had you installed a CS4 suite while you had a CS5 suite installed, you would have seen the same thing.