Mac OS X 10.4.6 released...

[eric2006]

Here's what mine looks like

Same thing for me.

 

[Veljo]

Strange, I remember it showing the Startup Disk for me a while ago, but here's how mine looks now under 10.4.6:

 

[chemistry_geek]

The startup disk may be indicated when other volumes may have the ability from which to be booted. My Mac indicates the current startup disk probably because I have several FireWire drives connected, including my 4G 40 GB iPod, from which I have booted from in the past (new USB-only 5G iPods cannot be startup devices ).

 

[ElDiabloConCaca]

I have only one bootable drive, and my "About this Mac" shows the startup disk, so I doubt it's due to whether or not you have a single or multiple boot drives.