It's about profitability and economy wise i suppose, if BTC is helping the economy, stimulating startups there is no reason to ban BTC as long the negative consequences like money laundering, tax avoidance doesn't impact that much i guess. Small government would embrace BTC like foreign investment/source of tax income while the ones with big GDPs would ban it to preserve their main economy, or maybe their population are too much to handle, it's pretty obvious if you check you legalization of Bitcoins in various countries on Wiki, its exactly how it is at least for now.
I think it will be more better for those countries whose currency has low value as compare to other countries currencies, although it will even be better and in favlour of all the countries to have a common currency and same value everywhere. But i think some big countries may not be in their favour. But i am sure that when they will realize their importance they will surely give more preference to bitcoin then and will turn it as legal currency.