I'd imagine most English-speaking internet users have gotten used to doing local-to-USD conversions. As someone in the US, I usually know about where CAD, AUD, and GBP are relative to me.
Even if you don't know the conversion, something in the range of 50-200% is a lot easier to adjust to, whereas Rubles are on a very different scale (1 GBP = 108 Rubles)
Obviously the ideal would be local listings, but USD is probably the most-familiar reference point if you have to choose exactly one
I have to agree.. given the amount of international business transacted in USD it's a pretty well known currency secondary in most of the world followed by EU then Chinese Yuan and GBP. That said, being in the US can't say how widespread rough translation values of Yuan are to most people outside the Asian/Pacific region.
Even if you don't know the conversion, something in the range of 50-200% is a lot easier to adjust to, whereas Rubles are on a very different scale (1 GBP = 108 Rubles)
Obviously the ideal would be local listings, but USD is probably the most-familiar reference point if you have to choose exactly one