Mine's only half as massive
(the link's in my sig btw)
if you look at the bottom of the totals, there are a few little icons of a ghost , a traded icon , and a... pinwheel thing
both of those mean either he doesn't own it any more, traded it with a friend, or he never did own it at all (sneaky pirate!)
which brings his owned game total down to a, still impressive, 345