The way the DMCA (available at http://www.eff.org/IP/DMCA/hr2281_dmca_law...1020_pl105-304.html) is worded, you can't sell products that are primarily designed to circumvent copyright protection. However for the criminal penalties to apply, you have to do this "willfully and for purposes of commercial advantage of private financial gain."
I gather that the jury was not convinced that the violation was willful and so found them not guilty. However note that Elcomsoft did have to stop selling their product in order to make this argument. If they had continued to sell it even after being informed that it was illegal, their actions would have been willful.
So the DMCA can still be used to stop people from selling this kind of software, but perhaps not in every case from criminally convicting them for it. That's what this decision seems to mean.