It should be quite clear that in this particular instance, Valve has decided that Bitcoin has utility as a transfer of value. You're questioning whether or not Bitcoin has utility as a store of value / unit of account. It appears that to Valve it does not, but there is also a chicken/egg issue with bootstrapping a new currency given that Bitcoin doesn't have sufficient adoption yet to complete a full lifecycle in terms of usage. That is - Valve has no use in holding bitcoins because they can't use them to pay their bills. This may change at some point.