Why bother trying to acquire them when there is nothing technically difficult about what opendns is doing and when google has more resources and technical expertise to bring to bear on the problem? What exactly would you expect opendns to bring to the table other than a trademark and a somewhat controversial reputation?

To be honest I am somewhat surprised that opendns has lasted as long as they have, but I expected the attack to come from the akamai/cdn direction rather than directly from google.