what speakers demand high end electronics

Most any good speaker will sound its best if matched to the right amp that is also of good quality.

Good quality and high end are not necessarily always the same thing in practice.

Many larger full range speakers require more power to be driven to the max. Generally, getting the right and good quality high power amp needed to drive these will tend to cost more in that it costs more in general to build a good 250 w/ch high current amp than a similar 50 w/ch one.

"By stating that Harbeth speakers work just fine with inexpensive amps, he removes an obstacle to the potential buyer, thus possibly making another sale."

Most successful speaker manufacturer's work hard to avoid creating obstacles for willing customers, not just Harbeth, I would guess.

Its probably a best practice in general for most companies so as not to limit their potential sales right out of the gate.

Since a lot of what people like or do not like is highly subjective to start with it does not make sense for a speaker manufacturer to make any stringent hard requirements regarding what you use their speakers with.

As long as the speakers are compatible and work with the gear and the gear is not likely to damage them, that's really all that is required at minimum.

But I would expect better vendors though would provide more detailed information that can help to optimize results technically for a customer if one asks specifically in help doing this.

Or if not, there is always your friendly audio sales consultant. They can provide more unbiased product options to the customer. The good ones will do whatever it takes to make sure their finicky customers get the best bang for the buck.