How about Command-Tab? There's only one way to access that functionality. How do you capture a screen in OS X without the secret "shortcut" keys or the command-line? How about ejecting a secondary optical drive? Zooming in and out?
There are a bunch of ways to eject a drive: 1. little eject button in Finder, 2. Right click on drive on desktop -> Eject, 3. Drag drive from desktop to Recycle Bin (this one is weird, but intuitive for long-time Mac users I guess). I admit I may be misinterpreting what you mean by "secondary" optical drive.
System-wide zoom is mega-situational. I'm sure it's useful for those with visual impairment, but I've never seen anyone use it nor have I had use for it myself. This is like complaining that high-contrast mode in Windows does not have an easy-to-access menu.
If I had two disk drives, I'm not sure which it would eject. I suspect that this is what WayneDB was referring to.
Capture a screen? Grab.app
Eject secondary drive? Drag it to the trash can.
You got me on the zoom in/out. I don't know that one. But I could make an argument that this one is not a shortcut, but the only command, as it falls under accessibility.