Why does "cvs status" send the entire file to the server (apparently)?

[Karr, David]

The connection to my cvs server is somewhat slow from where I am right
now, so I can clearly see when things are taking a long time.  I tried
running "cvs -t status -v" so I could see more details of what's
happening.  It appears that for each file it encounters, it is sending
the entire contents of the file to the cvs server (it says "Sending file
'...' to server").  Why does it need to do this?  This is especially
frustrating for large binary files, which take a long time to tell me
that they are "Unknown" to the server.