In terms of general computing it’s not true at all. Intel has designed their architecture so that even though they aren’t getting MHz faster they’re still getting a 10-20% overall performance increase every generation. It was looking to be true but Intel has developed a brand new type of transistor that makes it possible to shrink CPUs much smaller than they could have otherwise with traditional transititors. It’s actually incredibly cool watching how these guys deal with problems that occur when they try to shrink things to sizes they were never intended to go. When you get to the scale we’re at now nature itself tries to interfere, for example quantum tunneling, and it’s fun watching these guys develop new things to overcome it.
Now in terms of consoles, yeah there’s some truth to it. The problem is that they all use garbage IBM processors in consoles and IBM’s performance increases lately have been pretty stagnant when compared to Intel. They placed a lot of stock in the Cell processor and it just didn’t pan out like they thought it would. Now compared to the XBOX360, the Wii U’s CPU will be much faster but compared to the PS3 it will only be 15-20% faster. Actually, compared the 360 the Wii U could be up to twice as fast as they’re using the same server CPU that was used to power Watson. This is still significant in terms of games capability but it’s not enough to warrant building a whole new console to compete against, at least not for Sony. Considering that most high-end titles are actually playing at 720p on the PS3 and some lower weird scale on the 360 it’s likely that they’ll just be played at full 1080p on the Wii U since that would require no major change to the overall game. This sucks for Wii U owners as their games could be much better and will be held back by the previous generation but that’s been happening to the PS3 for a number of years now and is not a tactic that is going away anytime soon.