I set the main default for the website manually at the moment (and it's USD/bitstamp). For everything else there's just algo that decides this based on exchanges and currencies volume. I set what you see when you first enter website manually because otherwise it would be huobi/CNY and not many people want to watch that. When you enter the website second time, you are displayed what you have been watching lately. So newcomers see USD/Bitstamp, others see what they visited lately. But yes, when you click on the currency you see the biggest exchange for given currency first.
I'd like to provide unbiased data, that has nothing to do with my personal opinion. Maybe mtgox should not be default for EUR. *Maybe*. But I'm not sure. I'd rather be coding than keeping track of all exchanges news, especially when it seems really hard to be able to track down facts and not just people opinions. If I would use my personal opinion, btc-e for example would not be on the website anymore based on my support experience with them.
I think your work is impressive Kacper and it's amazing for me to read your very reply, thank you.
I think that it would help very much this community though, if you could consider adding an alert bar (even less colorful than this one
http://jsfiddle.net/joshnh/FxfHc/) when you are watching an exchange that is experiencing a state of crisis which could mislead people about the average value of bitcoin as seen across all the other exchanges, like Gox is experiencing now.
I would even appreciate if you would write on btce's page
"btc-e owners are unknown, trade with care" to the benefit of all newcomers but maybe is just me with this..
thank you,
John