You've posed an interesting question. I spent an hour or so trying to track down the answer and the best I can come up with is a guess - they are one and the same. Every single "G60V" reference I was able to backtrack (forum posts, reviews, manuals, parts, etc) led to an inconclusive dead-end, an anecdotal posting (which, if links were included invariably led to a G60Vx source), an official posting using a G60Vx designator, or a source that was obviously referring to the Vx but was either being sloppy or using "G60V" as short hand.
There are a number of reasons why the same units might be labeled differently - an administrative and/or marketing adjustment on Asus' part, adjustment due to placement in different sales markets (i.e...