/usr/bin/time

[Mark Wade]

I'm sure this is silly but can someone clue me in as to why these things 
are so:

 which time
/usr/bin/time

[22:04:08][markw]$ time --version
bash: --version: command not found
 
real    0m0.002s
user    0m0.010s
sys     0m0.000s

[22:04:27][markw]$ /usr/bin/time --version
GNU time 1.7

[22:04:41][markw]$

What is different invoking time as /usr/bin/time or time and is that 
true of other commands also?

-- Mark