I was part of BOCOG during the Beijing Olympiad, and I admit to not paying a huge amount of attention to what beverages were served/known. My feeling was, and locals told me as much, that the people didn't really see what the difference was between Coke and Pepsi BRANDS. But Pepsi is much better known as whole in the mainland because it was there before Coke due to Pepsi owning (at the time) KFC and Pizza Hut (which are both huge over there).
The thing that is strange here, that, again, the financial press opts to ignore is that Coke has a contract for exclusive worldwide rights to be the official soft drinks of the Disney Parks (there is a partial exception in Japan where Coke and Kirin split rights). I know Coke wanted this contract and expected it to expand their BRAND penetration in China. It just wasn't open because someone (Stanley Cheung, perhaps?) ordained that Pepsi would be the official soft drink. I'm sure that everyone who bothered to look at the press release that I linked to showed that Paul Candland's 'face' was played up and the big news of Stanley's HUGE new role at Disney was played down. Strange again?
And, yes, Pepsi was once served right alongside Coke at WDW and DL. Can you imagine going into a QSR at WDW today and having Coke, Pepsi, Tab, Fanta Orange, Fanta Root Beer and Sprite as your choices? Now imagine how workers would be able to figure out what cola-colored beverage was which. Yet, they did (only in some locations as some were Coke and Pepsi exclusive). This all changed in 1982 when EPCOT Center debuted and Coke first snagged the worldwide exclusive deal.