The thread title is hopeless... "Reusable Launch Vehicle concepts" would be better.
Space Shuttle is strictly ...
That brings to mind a thing about this English language, and language generally, words move, they change spellings, shift meanings, sometimes even reverse meanings. This English language has a many centuries history of specific terms becoming generalized.
For instance, the words meat, bread, fruit, have each had a term of being employed to mean food generally.
Space Shuttle, space shuttle, is now living that evolution.
Space shuttle is no longer strictly The Space Shuttle.
English language users are adopting it as the general term for a concept.
The language will do what its users do with it and there is no stopping such change, such evolution.
Related reading:
The books Words on the Move, and, Word on the Street, by the linguist John McWhorter.
The books discuss this phenomenon and others at length with many examples.
I believe comment is also made within them that while such change is happening in real time, some people will express their protests regarding said change via the certain irony of employing words which went through their own evolutions in prior decades or centuries.