The resigning info for Ninja Gaiden was released long ago on www.xbox-saves.com, don't know about the DOA series though.
Why wouldn't they want people to be able to transfer saves between Xboxes? Or, why do they not want people to be able to modify games they purchased? You'll have to ask them, I'm sure they have plenty of excuses: "Blah blah, copyright, blah blah, reverse engineering, blah blah intellectual property, blah blah blah blah blah"
Kinda funny, because if you ask a company like Valve, they will tell you that modding may be the only thing that kept them alive for years.