http://googlecode.blogspot.com/2011/08/native-client-brings-...
" The next milestone for Native Client is architecture independence: Portable Native Client (PNaCl) will achieve this by using LLVM bitcode as the basis for the distribution format for Native Client content, translating it to the actual target instruction set before running. "
I actually dislike PNaCL for a different set of reasons, but claiming it was built as an x86 sandbox, and meant to stay that way, is just revisionist history. If you believed otherwise, it was, in fact, your misunderstanding.