Bitcoin can't be centralized? Now I'm not sure what you mean by being centralized. Look, I already encountered two contradictory ideas about what Bitcoin decentralization actually is, so what is your take on this? If someone grabs more coins than anyone else, would this go for centralization? Or, rather, what could in this case prevent their owner from inflating Bitcoin derivatives if he decides to?
It's a long story if you're not familiar with Austrian economics, but as far as one person or group amassing too many coins, it can't happen for very long. Even if one guy magically had 90% of all coins, he could only enjoy this situation to the extent that he spends them.
I'm familiar with Austrians (sometimes even think myself belonging to them), consider their theory of subjective value brilliant (which started with Carl Menger). I know what you mean here, but, I'm afraid, this idea is not the only option in this case (and probably not the best one either). If that guy accumulated 90% of all coins he would be a central bank himself (remember, there is no other currency in circulation but Bitcoin). He wouldn't need to spend the coins, he could just issue "paper" BTCs, allegedly covered by real bitcoins. And then we have Gresham's law...
Why would people accept paper BTC? People accepted paper gold because they didn't want to lug around gold bars. Bitcoin has a weight of zero and is even easier to hide than paper bills.
He can only be a central bank if he uses his BTC to pay off government officials to get him special privileges. In a Bitcoin world, there is no central government, or only very weak ones.