Because in the past, the power of a machine was a particular selling point and of interest to the gaming community. Console gaming is a very, very new concept, and has only recenly began to fully mature. I believe it was Jobber who said that all we have now to worry about is lighting, as machines these days are powerful enough to produce just about anything.
Back in the days of the Sega Genesis and Super Nintendo, this was not the case. It worked more in Sega's favour at the beginning of the ultra-heated 16-bit war when the Megadrive exploded onto the scene before the SNES, as it was 'twice the power of the NES'.