Clearly the US Dollar is not the solo world currency anymore. Regional currency are emerging with the Euro and Yuan. But here is some interest points--
When China established regional Yuan trade, this only increased its USD reserve because they were not paying for import with USD reserves... ops on their part.
When the EU trades with Ukraine it is in USD- WHY- because its agriculture export is all in USD.
Article points out that USD reserves in Russia helps prop up the Rubble. Without $200B in USD, the Rubble would easily lose half its value.
As long as the Dollar is the currency of trade for Oil (and add grain), it will continue to be the primary world reserve currency. With the US dominate in Agriculture and now oil, USD will be around a while..
In addition to the points you made, the US is still the second-largest exporter in the world. Other countries must buy these exports with USD, regardless of its reserve currency status. The only exports from Russia that are viable on the world market are energy, precious metals, and military equipment (and most of the latter are bought on credit from shaky third-world countries). The US will likely become the largest oil producer in the world in 2016, despite the best efforts of the Obama administration to prevent this from happening. The US energy revolution has completely transformed the power relationships we took for granted in the second half of the 20th century. That is why Putin is grabbing what he can now; it's a defensive play for what portends to be a century of decline for the Russia of 1990.