Ultimately a review is an opinion, so 5 stars won't guarantee your satisfaction, particularly as there as so many variables such as the music you listen to, room acoustics, and synergy within the overall system. What the 4 or 5 star review does tell you is that a product meets a high standard and is well worth exploring as a possibility.
Regarding new products versus older ones, I'm not sure things move on all that quickly to be honest. For example, I've owned several highly regarded speakers (including MA BX2, B&W 685, KEF Q300) and, in my room the 1990s Mission 751s work better than any of them. I've also not heard any other standmounters below the PMC DB1i that produce the same atmosphere as the 751s. If I was writing a comparative review between the 751s and some of the newer options, I'd still give the 751s 5 stars.