I'm starting to suspect that one reason Axioms (among others) get branded as "bright" without having any apparent response peaks is that a number of nearfield monitor speakers (eg. the Rogers LS3/5a "BBC monitors" and in fact a whole generation of speakers) have a dip in that region. If you EQ to sound right on one of those speakers then your recording is going to be a bit peaky in that region... and on Axioms the recording is going to sound bright.
If you look at the measured response of enough speakers one thing you notice is that quite a few of them have a small dip in the 3 KHz region, including the Axiom M3/M40/M50 family. 3 KHz is, of course, right around the normal crossover freq for a small 2-way speaker. Alan pointed out that the M3/M40/M50s have that small dip because they use the 6.5" driver for midrange and its off-axis response drops off faster than the 5.25" mid used for M2/M22/M60/M80. The result is that on-axis response on the 3/40/50 is real good but in a typical room the off-axis response blends in and gives you that dip.
The result IMO is that M3/M40/M50 actually sound best on anything recorded to be extra bright (and sound just a tiny bit recessed on really good recordings) while the M2/M22/M60/M80 can sound a bit harsh if the recording is peaked up in the 3KHz region but sound exceptional on good, flat recordings.
I guess it would be better if the M2/M22/M60/M80 had a "flat" / "crappy recording" switch on the back
EDIT -- I should add that these comments are fresh from comparing M2, M3 and M60 together in the same room. I owned the M2s and M60s but at the end of the testing I decided that for casual music listening (eg. listening to whatever happens to be on the tuner or the CD changer rather than picking the good recordings) the M3s did have an edge. If you are picking and choosing what you listen to (ie no crappy recordings unless the song is really good) then the M2/M22/M60/M80 family will get the very most out of the music.
Again, all these differences everyone talks about are pretty minor (a few dB), we're not talking ski slopes in the frequency response curve. If you get a chance, poke around the Soundstage site and compare the response curves for M2, M3, M22 and M40, then compare them to other well-regarded speakers. The M3/M40 have a bit of the same midrange dip you see in the Paradigm monitor speakers, for example (although less of a dip), while the M2/M22 are pretty flat. The M2, in particular, is just scary flat until the bass disappears around 80 Hz
Bottom line -- yeah, the Axiom M2/M22/M60/M80 are going to seem bright on some recordings but as far as we can see it's the recordings not the speakers. The M3/M40/M50 aren't likely to sound bright on anything.
