Huh? Since when do you always use 'ls' after 'cd' - I can think of many times that I don't need to do this, and it would annoy me if every time I called 'cd' it then printed out the directory listing as well.

The popular Unix mantra is "do one thing and do it well" - both these commands, while definitely connected, are each "one thing" and they both perform them very well.