When upgrading to a new version of Ubuntu, it is necessary to install newer versions of most installed applications. A substantial fraction of packages will need replacing, because either:
- The new Ubuntu release contains a newer version of the package, or
- The package version is similar, but because libraries in the base system have been updated upon which it depends, it has been rebuilt to work with them
I'm afraid the answer is that using the short term releases (12.10, 13.04, 13.10) does require a relatively large amount of bandwidth to keep updated. If you don't want to update on a 6-monthly cycle (with associated bandwidth usage), the LTS version (12.04 and probably 14.04 when available) allows you to keep the base system for 5 years from release.