Well, as for the multiplication, it's not really in C++'s philosophy: languages like Ruby come "batteries included" and with the "principle of least surprise". They are intended to have lots of these little niceties as an above-and-beyond-the-minimum feature. C++ is a system level language which is intended to be "closer to the metal", which is abundantly clear in that a string isn't even a core data type of the language, but a library-provided addon. Even FORTRAN has a native string type, so you can see how low-level C++ is positioned to be. This is intentional: what if you're programming an embedded chip with 1K storage and have no use for strings? Just don't include 'em.
Anyway, it's not 100% clear what the multiplication operator is supposed to do. In other words, in the core language and libraries of C++, no feature gets in unless it seems that almost everyone would agree on the proposed functionality. It's got to be really universal.
I for one might think that "123" * 3 could give "369" - multiply any digits by 3. I further propose that this interpretation is "sane" enough to keep your repeat operator interpretation from being the only unambiguous interpretation.
The literal notation is far easier and more clear to answer: std::string is a part of the standard library, which is one level of abstraction above the language syntax itself. In other words, the literal notation would bust through the level of abstraction that separates "language features" and "the library that you can expect to be bundled with your compiler".
