I don't agree with the decision or with most of what Goodell does, but agree with Ovi that this was likely done out of liability concerns. At least some in the media agree:

Bob Labriola@BobLabriola[URL="http://www.planetsteelers.com/BobLabriola/status/314458372122501123"]17m[/URL] Re: crown-of-the-helmet rule, give the lawyers the win. This was about legal liability and lawsuits, more than the game of football