Well it has been true for ever, just look at every benchmark. AthlonXP's run at a lower clock rate but perform the same as Pentium4's at higher clock rates. I don't know why you consider that a lie or bs when the evidence is in every single review from every single reputable website on the internet
However, the latest AthlonXP 3000 is not as fast as even the Pentium4 2.8GHz, as AMD is falling behind, their manufacturing process is old and their die construction needs reworking. They've used practically the same plans from 800MHz up to 3000XP