Temporary jitters around pre-deal speculation. Some say the recent crackdown on illegal insider trading has hushed the takeover rumor mill. Some typical pre-announcement run-ups in deal targets haven't been there, especially with Berkshire Hathaway's bid for Burlington Northern and Stanley Works' bid for Black & Decker, says Jon Najarian of OptionMonster.com. "The rumor mill has slowed down considerably."

Trading volume has been relatively quiet in this year's takeover targets the day before deals, compared with targets in 2008, says FactSet Research, suggesting reduced M&A speculation.

It's unclear if the M&A stock pops will continue, especially with stocks hitting 2009 highs. In the fourth quarter so far, deal values have been just 27% above the stock prices of takeover targets, the smallest difference since early 2007, Dealogic says.

Nonetheless, the fact buyers are offering such a premium this year gives some comfort to investors. "If managements (of companies making buyout offers) are willing to put such a slug down and pay a premium, confidence is running high," says Jack Ablin of Harris Private Bank.