It's how you do it in many C++ implementations, but IIRC it's not actually mandated in any way unless you strive for GCC's IA-64 ABI compatibility (the effective standard on Linux for C++)
C++'s vtables are also, in my experience, especially bad compared to Objective-C or COM ones (MSVC btw generates vtables specifically aligned for use with COM, IIRC). Mind you it's been 15 years since I touched that part of crazy.
It is more the other way around, COM was designed to fit with how MSVC generates vtables.
It is a simplification of OLE, and by the time the idea came up to use that approach, there were tons of OLE code since Windows 3.1.
By the way it wasn't gone away, after how Longhorn went down, it became the main API delivery mechanism on Windows, sadly improving the tooling has never been a pritority other than half-finished attempts.
C++'s vtables are also, in my experience, especially bad compared to Objective-C or COM ones (MSVC btw generates vtables specifically aligned for use with COM, IIRC). Mind you it's been 15 years since I touched that part of crazy.