N00b Filesystem Question

[globalm]

Don't laugh - I know the answer will be obvious.

Can anyone tell me why, when I start a terminal, then SU and enter

cd /sdcard/
ls

I get to see everytning I expect on the SD card.

BUT

If I boot to the Recovery ROM, access the phone with ADB and do

adb shell cd /sdcard/
adb shell ls

I don't see any files at all?

Some kind of virtual filesystem going on in there?

Just curious.

TIA