These were changed and standardized in CS4 across all aspects of the UI and all languages. The default shortcuts are now CNTRL+2 to Show All Channels with CNTRL+3 Showing Red, CNTRL+4 Showing Green, and CNTRL+5 Showing Blue. The change was made, in part, to help non-English users.
Photoshop used the keyboard shortcut cmd + ` to select channels for years prior to OS X adopting it as a shortcut to cycle through open documents.
We actually changed this behavior in CS4 because lots of users requested that we respect the OS convention of using Cmd + ` for cycling through open documents. After we made the change, many longtime Photoshop users complained that they wanted to old behavior back to fit their shortcut muscle memory.
Thankfully, users of Photoshop CS5 and CS4 can customize this behavior to their liking:
In Photoshop CS5, launch Photoshop CS5 and choose Edit>Keyboard Shortcuts... then check the option for "Use Legacy Channel Shortcuts." Restart Photoshop CS5 for the change to take effect.