That's not a C++-ABI but a C++-as-compiled-by-gcc-ABI. C++ itself does not define an ABI and different compilers (sometimes even from the same vendors) will use different incompatible ABIs.
It is the linux standard C++ ABI as the defined by the linux standard base. An ABI for low level language is necessarily (OS, architecture) specific, so you can hardly do better than that. There is no ABI that could be usefully defined at the standard level (and even if it somehow were, it would be mostly ignored[1] as compilers wouldn't break compatibility to implement it).
[1] I could see the committee standardizing some intermediate portable representation requiring installation time or even JITing in the future though.
It is not the linux standard C++ ABI, it's just the defacto standard ABI because of gcc's former dominance and clang intimidating the ABI. And I broke things in the past, where I had to recompile stuff, due to different compilers (clang, clang+libc++, gcc in different -std=c++ modes) producing not 100% compatible outputs.
You can say it's good enough (most of the time), but it isn't really a standard, unless I am mistaken.
The Itanium ABI it is not just whatever GCC does; while it is not an ISO standard, it is an intervendor ABI documented independently of any compiler implementation and changes are agreed among compiler teams. It is continually updated to track the C++ evolution.
The standard library ABI it is not covered the the Itanum ABI (outside of some basic functionality), but it is defined necessarily by the platform. For linux that would be libstdc++.
The LSB references the Itanium ABI and defines libstdc++ as the ABI for the C++ standard library on linux platforms; it is again not an ISO standard, but it is as close as you can get on Linux.
And of course the C++ ABI being a very complex and both the ABI document itself and compilers have bugs from time to time, especially if you live close to the bleeding edge.
although it might the facto be, at least for AMD64, I wouldn't say it is the official standard ABI of all unix systems. But it is the standard ABI of Linux based systems, at least those that claim to conform to the LSB.
There's more to a practical language ABI than stack and vtable layout. If you write idiomatic C++, this means passing objects from the standard library around. If different compilers use different implementations of the standard library that aren't layout-compatible, things break.
The Linux processor-specific ABIs explicitly call out that the Itanium ABI is the C++ ABI for x86 and x86-64; ARM has its own ABI that differs from the Itanium ABI only in the exception handling details.
