Your blood is 92% water. Seawater is somewhere around 95% water. Despite being incredibly similar, replacing one with the other in any great amount would be catastrophic. You share half of your DNA with a banana, but you're still completely different from a banana in any way anyone cares about.
The fact that Prolog, Fortran and Ruby are all Turing-complete is useful to know from a computer science standpoint, but from a perspective of actual use, it just isn't that relevant. A language — whether human or computer — isn't just about the algorithms it can express, but about the ways it lets you express them, understand them and combine them. And Turing equivalence tells us very little about that sort of thing.
This is a bit abstract, so here's a tiny but concrete example of how differences in how you express an algorithm can have a tangible effect:
f = open("somefile.txt")
f.write("Hello world")
f.close()
with open("somefile.txt") as f:
f.write("Hello world")
They're effectively the same, and could conceivably even be compiled to the same object code, but the latter is less error-prone — we can't accidentally leave the file open. A language that only allows the former is inherently more brittle. There's a whole world of variation like this (and also a lot unlike this) that doesn't affect whether the language is equivalent to a Turing machine, but does have a real impact on your program.
So I think it is quite possible for languages to be worlds apart while still being able to compute everything a Turing machine can.