A common motivation for acquisitions is to buy users, not technology. YouTube used PHP and the video tech in flash - but they were the ones to grow the userbase (and continue to do so). If Summly had the product/marketing to be popular and growing, that's why Yahoo bought it. (though it seems Summly doesn't have the strong network-effects of YouTube, of gaining both producers and consumers).

EDIT they could be buying market-product fit...? but yes, if they killed it... hmmm...