There is nothing inherently visual about computing.
Digital processors read their instructions from files or streams of binary text.
Talking Tux needs the phonetic intonation string, then these missives could as easily be spoken. However, most computer users are intensely visual creatures. We may expect the situation to change if there is a demand for auditory web browsing, on car phones for example. But until it does, eyes free computing will likely continue to be based on modifications and tweaks to existing technology. This paper gives a general overview of the open-source software techniques that can be used to bring speech to Linux.