IIRC, both Adobe Reader "Protected Mode"[1] and Chromium "sandbox"[2] are built on Windows user-mode sandbox framework[3]. Basically, things like principle of least privilege and disable writes etc.
Security is all about execution: Chrome has an enviable track record; Adobe has an embarrassing one. They could change that but it's unclear that they're motivated to build up serious security competency (if they were, the manager in charge of their update process would be fired for cause)
[1]http://blogs.adobe.com/asset/2010/10/inside-adobe-reader-pro...
[2]http://dev.chromium.org/developers/design-documents/sandbox
[3]http://blogs.msdn.com/b/david_leblanc/archive/2007/07/27/pra...