The Nyquist-Shannon theorem states that exact reconstruction of a continuous-time baseband signal from its samples is possible if the signal is bandlimited and the sampling frequency is greater than twice the signal bandwidth. http://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem
Of course, real world implementatiosn of math suffers from some approximation....you can't have "infinity" in the real world (unless you are Buzz Lightyear). In practice designers build digital gear to a level that they believe makes the imperfections inaudible. Some engineers believe that digital audio is now into marketing hype territory (192 KHz, 24 bit and SACD formats are overkill) and that further improvements are not justfiable, as redbook CD imperfections are already dwarfed by other factors, such as the speakers and electronic imperfections. The popularity of lossy MP3, shows that many consumers must share his view.
Perfect analog, if it were possible in the real world, would no doubt be slightly better than the current digital implementations. However, in practice, given the current view of engineers and consumers, it seems unlikely that a new analog medium will be forthcoming. Necessity is the mother of invention....and the need just doesn't seem to be there.