Standby time is a bit like those video recorders that can be set to record a programme 1 year in advance. It might look great in the glossy brochures, but in real life it is of little relevance.
Notice how quoted standby time is always preceded by 'up to'. More often than not, standby time is tested without the sim card installed. But they never tell you that. Anyway, most people - who actually use their phone - will charge it every 2 or 3 days anyway. The point of a 2 or 3 week standby time is then fairly irrelevant. Unless the point is that "it was much better in the old days".