Most high-quality loudspeakers are 4-Ohms

high quality is relative. There a number of so called "high quality", speakers (4 ohms) that sound like a piece of sh%^*

Unsound- OP was, I thought, talking about 4 ohm nominal vs anything higher. See for example, his recent response:

When I had relatively cheap amps, I could not find anywhere about power ratings (RMS) mentioned for 4 ohm in their specs. All were listed for 8 ohm.

In that context, Vandersteens are mostly spec'd, IIRC, as 6 ohm minimum and would qualify as higher impedance (i.e., higher than 4 ohm) loudspeakers. Of course, you and I could disagree about lots of things audio, but I don't think that we would disagree that the speaker makers I put forward are generally considered "high end".

And to the OP, the post I quoted is very telling. What you are seeing is that in-expensive solid state amplifiers often lack the robust power supplies necessary to allow them to deliver high quality specs into a 4 ohm or lower load (many speakers exhibit lower than spec'd impedance across at least a part of the audio spectrum).

Any 4 ohm little monitors out there that can out do the 15 ohm Rogers LS3/5.♫

Swampwalker, I suppose for the most part we actually do agree. The Vandersteens aside from their selfpowered subs have a minimum impedance range of 2 to 5 Ohms. As for the others, yes they are generally considered "high end". I just haven't heard any high minimum impedance speakers that I would care to own, so IMHO I guess I wouldn't consider them "high quality" regardless of the craftsmanship, marketing, etc. involved. Others are of course welcome to disagree. I think the OP's question has more merit than some might at first assume.

16ohms or or so can sometimes be better sounding. And a easy load for most all amps. 4 ohms is easy to design for try keeping a 3 way or 4 way loudspeaker 16ohms not a easy design chore. But to be fair 4 ohm designs can sound great as do 8 ohm or 16 ohm. Just depends on total design and system said loudspeaker will be used in. In loudspeakers its the design and parts used that maters most the ohm loads more a issue when selecting amplifier.