i only see mobile version on Poloniex and not with bittrex or yobit ( i only use 3 exchangers ) but now i use tabtrader apps to trade in bittrex and poloniex
bittrex is created to be a responsive website so it's will be mobile friendly even there's no specialized app for bitcoin and the app will not going to be a problem because their users still could access bittrex perfectly using mobile phone due to responsive design,so don't having mobile app doesn't mean it can't be accessed from mobile
It's not native but i don't mind it. The site has nice features (richlist, ajax notifications) and they don't stop making it better.
So far they are a better Cryptsy, then Cryptsy could ever be.