It should be possible to create a plugin that would display PDFs in such a way that the Acrobat plugin would be used.
From our perspective, we like Google Docs better because it works across platforms, Windows, Mac, Linux, and mobile. Many or most users of those non-Windows platforms won't have Acrobat Reader, or its plugin.
Also, I do seem to remember the Google Docs Viewer having the ability to search within a PDF.