Greater current, better speaker control, higher damping factor of solid state amps and push pull tube amps, all lend themselves to your observation.
And the extra power also translates into extra headroom that lets those musical peaks through unhindered. My Horn Shoppe horns and Abbys never sounded better than when driven by a Sophia EL34, and a Golden Tube Audio SE-40, as compared to an Audio Note Kit1, and another 8 watt PP tube amp -- with the exception of the fully modded Clari-T, which really did the trick for the Abbys.
I remember back in the 70s when I was in high school and would go down to the local high-end audio store to listen to the Klipschorns driven by a Mac 200-watt tube amp. I don't remember the model of the amp, but it had a pair of blue backlit power meters (not VU meters) on the front and you could clearly see that while the power levels for normal listening were on the order of tenths of a watt, the peaks could easily jump to 150 or 200, if even very briefly. And this was with a speaker rated at something like 104dB. So, when you're 1.5, 3.5, or 8 watt amp tries to play the same music through the same speakers, something has to give when those peaks come along, even though any of those amps would drive those speakers more than sufficiently well.
That said, I'm with you guys 100% on all of this and have a pair of the Sig 70s (in Louis's cabinets) and a pair of Revolutions on order, and I've sold off all the other equipment except the Clari-T and my CDP.
Sure would love to talk to more of you in person -- dmason, richard, zls, srayle, and others, and if you're coming to RMAF, maybe we can find some time to hang out? I've been reading the Dark Star thread, plus lots of others on this forum and RWA as well, and find you guys very tuned into much the same kinds of things as myself. Can't possibly get away with OBs in this house, but it's all really interesting nonetheless.
Keep the great discussions and comments flowing!