This is a very relevant question, as there apparently is no Adobe Reader for OSX 10.6.4. The Adobe downloads page lets you choose versions up to 10.6.3, but apparently for no version after that. Supposedly it is because Apple Preview is able to handle plain reading, but whenever you encounter something a little bit smarter (like aspx files etc) it seems you still need Adobes version. I'm starting a new thread on this. Best regards.
Supposedly it is because Apple Preview is able to handle plain reading,
That's not it at all (not sure where you may have heard that).
It's more than likely that the verbiage in the download area hasn't been updated yet).