they probably have a lot of really advanced crypto (considering rijndael is only approved for i think secret level, i think).
AES with 128, 192 or 256-bit keys is approved for 'secret' stuff, but only 192 and 256-bit keys are approved for 'top secret'. As Wikipedia says, maybe the NSA thinks there's something wrong with AES with 128-bit keys, or maybe they're just being careful.
(Unnecessary reference: CNSSP-15: National Policy on the Use of the Advanced Encryption Standard (AES) to
Protect National Security Systems and National Security Information, http://www.cnss.gov/Assets/pdf/cnssp_15_fs.pdf [PDF])
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AES with 128, 192 or 256-bit keys is approved for 'secret' stuff, but only 192 and 256-bit keys are approved for 'top secret'. As Wikipedia says, maybe the NSA thinks there's something wrong with AES with 128-bit keys, or maybe they're just being careful.
(Unnecessary reference: CNSSP-15: National Policy on the Use of the Advanced Encryption Standard (AES) to Protect National Security Systems and National Security Information, http://www.cnss.gov/Assets/pdf/cnssp_15_fs.pdf [PDF])