Not the M60, but on the M50 and M3 it is part of the design, so no accusations are needed.
And yes, any larger cone will "break up" when tasked with playing too high a frequency. Break up is a form of non-linear distortion that is caused by flex in the cone.
If those speakers only had mid-range drivers and no tweeters the distortion may be more obvious. But with the tweeters playing, and the already diminished output of the large cone rolling off because of it's inability to play those high frequencies, very little of the distortion is audible.
The rest of Axiom's line uses band- or low-pass filters on their mids.
