Well CS2 development stopped as CS3 development started.
The best example of this was when I did my upgrade of the Canon XT to the Canon 40D just last year (or was it two years ago now?)…at the time I was using Adobe Photoshop CS2 to process my files. The reason? Camera file formats! As camera vendors develop new proprietary formats for their raw file formats (CR2 for Canon and NEF for Nikon as the two predominant players in the game), the need has always existed to update your software to accommodate the new formats for body upgrades. Just as a new camera body can necesitate the need for larger memory cards, hardware upgrades can also come with software upgrades. For many of us, an upgrade of one element in our tool kit comes with many unforeseen consequences and additional expenditures.