It's back to the drawing board for stock exchange companies Deutsche Börse and NYSE Euronext after the European Commission blocked their merger plans. German commentators ask if the megal-deal was even a good idea in the first place.

Wednesday was "a black day for Europe and for its future competitiveness on global financial markets" -- at least if Deutsche Borse is to be believed. That's how the Frankfurt-based stock exchange operator reacted to the news that its planned merger with NYSE Euronext had been vetoed by E.U. antitrust regulators.

Investors, however, seemed unperturbed by the news. On Thursday, shares in Deutsche Borse were even up by over 4 percent at times, trading above €47 ($62), amid expectations that the company would return cash to shareholders. NYSE Euronext's shares fell by just 0.5 percent on Wednesday. The consequences of the failed merger are not as bad as the companies would like to paint, it seems.

Announcing its decision on Wednesday, the European Commission, the E.U.'s executive body which is also responsible for regulating competition within the bloc, argued that the combined company would have had too much power over trading in European derivatives. Together, the two companies control more than 90 percent of the trade in European exchange-traded financial derivatives through their Eurex and Liffe exchanges. The firms argued in return that a large portion of the trading in derivatives does not take place on exchanges, but in direct or over-the-counter (OTC) trading between banks.