It is not Apple's mistake, this has been the procedure since the release of Lion, Mac OS X 10.7.
The user has been advised many times on here that the wise thing to do is, go to System Preferences > App Store and make sure Install App updates and Install OS X updates are NOT checked. That way the installer will not initiate until you tell it to do so.
After the Install OS X finishes downloading, go to your Finder > Applications folder and make a copy of Install Mac OS X in a safe place, such as your Documents folder. That way you will be able to keep a copy after the installer completes and self-erases.