All packages on an amd64 Ubuntu installed system are amd64 unless explicitly specified otherwise.
Packages that are listed as
*-i386 are compatibility packages for the
amd64 architecture which are usually needed as a dependency for an installed package.
This way, you can install a package that is available for the
amd64 architecture (the
amd64 version of an
i386 package) which is written for
i386 without having to "add" this "
However, if a package is listed as
*:i386, it is an
Certain packages are only available as an i386 version. This seems to be more common with proprietary packages and so wine is often an issue here as we all know how windows won't run a lot of stuff without the x86 (32 bit) directory.
With that said, I believe the i386 foreign architecture is enabled by default on newer versions of Ubuntu.
You can remove the i386 versions of all the packages on your system, although, you should do so with caution as this can cause compatibility issues with applications such as Wine.
Rest assured, however, that Ubuntu and apt will always default to and install the
amd64 version of a package over the
i386 version (except for Wine). Typically, you must specify the
i386 version and if no arch is specified, the system will almost always install and use the
amd64 version if one is available and or installed.