I always saw milking in videogame terms as consistantly releasing a title from a franchise Yearly. Nothing to do with how much it sells or how good it is.
The Mario name being slapped across 20+ games in 5 Years, just so it sells more? I see that as milking the Mario brand name. Call of Duty getting Yearly releases? I see that as milking. Singstar getting 987557 releases in 10 Years? I see that as milking.
Obviously there are some games that bypass the rule, FIFA, Madden, MLB, Etc