If you remove the wc -l (which just means count how many lines are in the output) you can see the difference ...
With vmquery -pn Scratch you get output like this (I am only showing 1 tape)
================================================================================
media ID: R0TP02
media type: 4MM cartridge tape (9)
barcode: --------
media description: Added by Media Manager
volume pool: Scratch (4)
robot type: TL4 - Tape Library 4MM (7)
robot number: 0
robot slot: 3
robot control host: womble
volume group: 000_00000_TL4
vault name: ---
vault sent date: ---
vault return date: ---
vault slot: ---
vault session id: ---
vault container id: -
created: Fri Feb 24 09:14:49 2012
assigned: ---
last mounted: ---
first mount: ---
expiration date: ---
number of mounts: 0
max mounts allowed: ---
================================================================================
With vmquery -b -pn Scratch
media media robot robot robot side/ optical # mounts/ last
ID type type # slot face partner cleanings mount time
-------------------------------------------------------------------------------
R0TP02 4MM TL4 0 3 - - 0 00/00/0000 00:00
wc -l just counts the lines, so with -b, you get the 'brief' output, less information, all on one line.
You didn't need to log a question for this, you could work it out by running the command without the |wc -l, and then with and without the -b option to see the difference.
Martin