My opinion is that bi-wiring is another hoax to charm those bucks out of your wallet.
Loudspeaker manufacturers don't care how much we spend on cables. They're the ones who decided their device should be bi-wired, but they don't sell cables do they?
Well, speaker manufacturer's customers are the ones who really make the decision for them. If you customer demographic wants to bi-wire, even just perceives the capability of bi-wiring as 'cool' or 'high-tech' even if they never use it, then a speaker manufacturer would be making a bad business decision to not put an extra set of input jacks on the back, regardless of the technical or auditory merits.
When bi-wiring, the conductor serving the mid-range driver is carrying far less current than the conductor serving the woofer. The difference is at least an order of magnitude, maybe a couple. Is the signal affected differently in either case? Many people say yes, but some people say no. You just have to listen for yourself.
Bi-
wiring comes in two flavors:
A) Bi-wire can be a second set of speaker wires running from the same amp to the same input jacks on the speaker. You could quintipla-wire if you wanted to.. and yes the current carried in each wire is cut in half each time you double the wires, but do you really think the sound is being limited by the ultimate current carrying ability of your first set of decent gauge speaker cables?
B) Bi-wire can also be a second set of speaker wires running from the same amp to a second set of input jacks that would normally be bridged to the first set (take out the bridge and wire to both input jacks). That just moves the bridge point back to the amplifier output jacks, and is typically not why the manufacturer puts a pair of bridged inputs on speakers (other than for marketing purposes)
Both of the above just add more wire.
Bi-
amping comes in two flavors too:
C) Similar to B) above, Bi-amping uses two sets of speaker wires running to two sets of input jacks on each speaker that would otherwise be bridged (take out the bridge and wire one set of cables to each input jack pair). But now each set of wires goes to it's own amp. This just allows more amp power since you are now using two amp channels per speaker instead of one. Real world effect? You could run a different amp for the bass that the top end if you wanted, assuming both amps have the same gain. Also, if you were to clip the amp running the woofers, your tweeters would not be affected. Each amp is still amplifying the full frequency range and the speaker is still doing the crossover duties. There might be a slightly easier impedance load seen by each amp, or there might not, but them's details.
D)
The speakers are modified to entirely remove or bypass the crossover (or a significant portion of it). This eliminates most components between the amp and the driver. An active crossover stage is added before the amplifiers to split the frequency range before amplification. Each amplifier then amplifies only the frequency range needed for the driver(s) it feeds. Most importantly, the load seen by the amplifier is definitely less complex and
much easier to drive since the frequency spitting and driver balancing is done on line level signals and not speaker level signals, so you can use much smaller amplifiers to do the same job. This works well and it's how huge PA systems are designed and how better 'active' monitors work where the active x-overs, amps, speaker cables and drivers are all in the same box. But it's rather complicated to implement properly with a standard speaker. You need test equipment to really setup the crossover correctly and it's
WAY easy to fry things if done wrong.. which is why you won't find this option common with speaker manufacturers unless they are doing all of it themselves 'in the box' of an active monitor.
Those are the facts.. and here's a (widely held) opinion:
Speaker manufacturer's are probably thinking about C) above. It's relatively simple and foolproof to implement, might actually make some real improvements at times and satisfies the tweaky audiophile crowd. If customers want to do B) that's fine with the manufacturer, even if it just adds wire. If they want to do D), where the
real gains are to be seen, they're on their own (to hell with the warranty).