The reason these overclocks are significant is that the Phenom wasn't able to reach the clock speeds that AMD originally expected it to, and that's one of the reasons it's had such a hard time competing with the Core 2. They were expecting to be selling 3 GHz Phenoms soon after launch, but the first Phenoms to ship were only 2.3 GHz, and even now the fastest Phenom chip is a 2.6 GHz part that struggles to overclock much past 3 GHz or so regardless of the cooling that's used. Even though clock speed by itself isn't a good indicator of performance, especially when comparing different architectures, if a processor was designed to be competitive at 3 GHz and they're only able to get it to 2.6 GHz reliably, that's a big problem.

If AMD has solved their clock speed limitation issues with the Phenom 2, that may help put them back on track to being competitive again. It's still too early to start celebrating until we see benchmarks, but it's good news nonetheless.