Prior to Mac OS X Lion, all Macintoshes came with a grey restore disc that contained the specific version of Mac OS X that the computer came with... for example, an iMac that came with 10.6.4 preinstalled would also come with a DVD that had the installer for the special copy of 10.6.4, which would only be installable on that certain iMac model.
With Lion and onwards, the installer is re-downloaded off the recovery partition when needed, and is still specific to the computer, but the version of the Mac OS X installer that you download from the App Store is installable on any computer. 10.9.1, for example, is installable on any computer that supports 10.9; but 10.9.1, as it stands now, will NOT be installable on new computers released this year. New computers coming this year will come with the version of OS X that is the latest at the time of manufacturing. For example, let's say the Mini is released in late February. Either 10.9.1 or 10.9.2 will come preinstalled with the Mini, and the redownloadable version from the recovery partition will be specific to that Mini; if you want the full (aka; all computers-version) of the Mavericks installer, you'd have to "buy" it from the App Store (free) or re-download it if you have already "bought" it.
Long-winded, I know. tl;dr edition: there are certain versions of the OS X installer that's only designed for certain computers, but the actual install process is the same, it's just the drivers that are included are specific.
