Can all Mac executables be copied between machines? Many programs for OS X simply ask to drop the executable into the Applications directory. This obviously means that copying the executable onto another machine is possible without problems.

What about applications that go through an installer (for example iWork) - do these do something extra? Can I simply copy the Pages executable onto another machine and have it run?
No

If the application requires an installer, it needs to be installed on each machine. This includes pre-MAS (Mac App Store) iWorks and Microsoft Office 2011 for example. 

Only applications that were not downloaded from the MAS and explicitly specify installation by copying the executable can be copied between machines.

Applications purchased through MAS can be copied between machines as long as the user logging into MAS on the target machine is the same user that originally purchased the application.