Why "lsusb" return nothing?

I entered "lsusb" at the command line (as root) and nothing is return,
not even any error message.

Doing a strace the last few lines are:

open("/dev/bus/usb", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = -1
ENOENT (No such file or directory)
open("/proc/bus/usb", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = -1
ENOENT (No such file or directory)

What happened?

This is Ubuntu 10.04 (it used NOT to be like that, not sure I what did
wrong last time).   But running a VirtualBox INSIDE this same OS, I
was able to get result from "lsusb" (after enabling the USB devices in
VirtualBox interface) and strace gives result:

open("/dev/bus/usb/001/002", O_RDWR)    = 3
ioctl(3, USBDEVFS_IOCTL, 0xbff6f75c)    = -1 ENOTTY (Inappropriate
ioctl for device)
close(3)                                = 0
open("/dev/bus/usb/001/001", O_RDWR)    = 3

Why the difference?

--
Regards,
Peter Teoh