It is nonsense. Length differences in speaker cables are inconsequential in normal domestic situations (unless they are on the order of a kilometer)
The difference in length on the sound is so minor as to make my head spin that any company would suggest such nonsense is important.
A nice 'theory' but in practice it does not matter.
I do think my three channels are pretty close to the same, just by coincidence. Then the back are ten times the distance of wire, because they have to go around the whole room.
PS if the length of the front being equal are so 'important' then why not the rear in addition? answer: because no one would bother!!
Actually, from a speaker cable manufacturing perspective, I would strongly state that all the cables in a surround sound system should be the same. Better yet, if you are ever going to contemplate adding speakers to another room, the cables in your surround sound system should therefore be matched to that future potential length as well. That is why I strongly suggest consider putting speakers in your back yard, ideally at the point on your property as far away from your house as possible - ya know, so they speakers can face the house and not annoy the neighbors so much. And yes, when doing this, all your surround sound speaker cable should be upgraded to match these lengths as well.
If you have any questions, just send me a blank signed check. Granted you will never hear any difference if you don't head my advice, but its a great revenue source theory at least.