Expect: tcl/tk
Watir: Ruby/WET
There are not many good reasons to nail these good/powerful tools to specific languages and restrict it's wide spread usage. On the other hand, nailing them to language gives the marketing muscle to tag on to existing bandwagon. Both products (Ruby/Watir - Expect/tcl) get cross promotion benefits. From a person who don't know both, it is additional thing to learn - instead of reusing sh and perl...