Ubuntu is not a tailored operating system under the definition that I know. Tailored operating system are usually specifically designed or modified to run a single piece of hardware. The words "embedded system" are usually thrown in for good measure.
The most clear example of a tailored operating system would be an OS designed to power a PDA or similar device and which has only those elements required to correctly operate the device. This might be a modified version of Linux (eg TomTom GPS), Windows (eg various PDA implementations), Android (notably Phones) or any other horizontally deployed operating system (eg many Ebook readers with code compiled to run on low power processors.)
You could possibly argue that the linux kernel, when compiled with modules designed for a specific device might comprise the core of a tailored operating system, however I don't think that you could argue that Ubuntu as an OS product fits this definition.