I'd agree with that, there's also the consideration that success in one generation leads to success in the next. The PS1's market dominance gave the PS2 a huge leg up due to backwards compatibility as well as name recognition, and conversely the failure of the Saturn really dented the chances of the Dreamcast. The Xbox 360 is doing fairly well, but it didn't have a huge amount of momentum from the original Xbox.

The NES' success and market dominance set up Nintendo for a second round win with the SuperNES and I think strongly contributed to the GameBoy's success, and Nintendo's been riding that wave ever since, carrying them through two systems that were relative failures.

Comparatively, while the Atari was hugely successful in its own time, it wasn't enough to make the 5200 and 7800 successes. The PS2 similarly is a bit dampened in success as Sony entirely lost momentum, and I'm finding the PS2 sticking around to be rather similar to the 2600 sticking around and encroaching on the sales of its successor.