User blog comment:DirgeOfCerberus111/Adeptus Custodes Vs. Grey Knights/@comment-3398633-20110819134323

It could also be explained this way. While the the Secret Sevice is quite fomidable, they aren't trained nor could they hope to fight war. The Navy Seals on the other hand, are the superior to the Secret Service, and could do their than they could. Likewise with the Custodes and the GK.