Is there any difference code wise to the RTM (specifically windows 7 RTM) compaired to the final Boxed Product?
There shouldn't be.
The RTM (Released To Manufacturing) release is what will become the final boxed product. It's the version of the software that's going to be pressed onto disk. It's also the version that will go to hardware manufacturers so that they can have Windows-7 machines on sale from the launch date and onto the MSDN subscribers downloads page so developers can make sure their applications work with it.
They are always the same unless a serious bug is found with RTM partners, in which case they usually release a second RTM edition or a quick hot fix that gets bootstrapped in setup.
Well, I believe this is how it is meant to be in theory. (I asked something along the lines of, what happens if we find a bug or something that didn't get picked up in beta/RC's at a Technet event).
No, there isn't. RTM & General Release have the same build number: 7600. As Microsoft says here:
The RTM code will be delivered to our partners within the next few days who will then start preparing to deliver some amazing new products timed to hit at General Availability (GA) of Windows 7 on October 22nd.
regarding Windows 7, there is no difference between 7600.16385 and the upcoming retail version.
No. They are the same.
The "Release To Manufacturing" edition is literally what is manufactured and placed inside the box (or digital distribution service, if applicable).
Updates should handle any minor errors, and major errors shouldn't exist - that's what the public RC was for.