Ottawa’s surprise rejection of the bid by Malaysia’s state energy firm Petronas to buy Canada’s Progress Energy Resources Corp. has everyone asking what it means for the deal that really matters: the proposed $15.1-billion takeover of Calgary’s Nexen Inc. by state-controlled China National Offshore Oil Co. The government didn’t explain its reasons for saying no to Petronas, and Canadians from many quarters have been calling on Ottawa to clarify the rules for assessing future takeovers to give buyers a better sense of their chances.