Interesting point. I know in the US, Bitcoin also is taxed as property to get around it not being considered a legitimate currency (due to the lack of government backing).
As far as the government holding the Bitcoin,I would imagine that they would be converting it immediately to their currency, so the Bitcoin would then be held by the payment processor.
That being said, I never thought of the impact of a single party just collecting a cut of every transaction from a finite pool of resources. I know Bitcoin are constantly being released into the pool - however I believe the cap of 20 million will be reached next year or maybe 2020 - I forget which one.