A final type of convertible virtual currency activity involves a de-centralized convertible virtual currency (1) that has no central repository and no single administrator, and (2) that persons may obtain by their own computing or manufacturing effort.
This is the provision which applies to Bitcoin and miners.
A miner doesn't have to be considered a creator. He merely needs to obtain his Bitcoins (or other virtual currency) by his "own computing effort" (people pooling their computing efforts will almost certainly be covered under this provision, too).
I don't think it matter because miners cannot remove coins from circulation so they are not administrators. If Amazon coins start getting issued Amazon can create and remove coins from the system so they are the administrators.
No-one's arguing that miners are administrators. The central issue with the potential to affect miners is them being classified as money transmitters if they sell their coins.
Different provisions apply to Blizzard (most certainly an administrator) and WoW gold than to Bitcoin. WoW gold would count as (b) Centralised Virtual Currencies and therefore the provisions of that paragraph would apply to Blizzard. Bitcoin counts as (c) Decentralised Virtual Currencies and therefore the provisions of (c) apply to Bitcoin, miners, and exchanges.
Off course an interesting question is how it would come to the attention of regulators that you're selling BTC you mined. Exchanges don't require you to disclose the origins of the BTC you're offering for sale, and wouldn't have the resources to verify any declarations by customers about such origins anyway - are they going to be required to report every single BTC deposit just in case you're selling BTC you mined as opposed to BTC you bought or received as payment for goods/services?
Also, bear in mind that this is a guidance statement. It tells you how FinCEN intends to approach the issue of virtual currencies but it doesn't create legal definitions in and of itself.