That .kext is also responsible for verifying some sort of signature in a hardware chip only present on genuine macs. See http://en.wikipedia.org/wiki/Apple%E2%80%93Intel_architectur...
DSMOS.kext has another function, however; it is involved in Apple's binary protection scheme[2] for certain OSX binaries. Essentially, OSX ships with certain important binaries (such as loginwindow, SystemUIServer, Finder, and Dock) that have certain vm pages encrypted. Decrypting these pages for use requires DSMOS.kext.
[1]: http://osxbook.com/book/bonus/chapter10/tpm/ [2]: http://www.osxbook.com/book/bonus/chapter7/binaryprotection/
There's just an outstanding myth that Macs still use TPM...