Are Speaker Cables Longer than 6 FT. Superior?

Hello,
I am puzzled!
I have read from a few sources that speaker cables 8 feet or longer are sonically superior to their counterparts that are 6 ft. long or less.
Granted, a couple of the sources that I read the info from were either cable manufacturers and/or companies that sell cables, or have them made for them, such as from the latest Mapleshade catalog, etc.
I do not understand how this could be possible.
Longer cables would have more dielectric coming into contact with the signal conductor, more opportunity for the signal to come into contact with EMI/RFI, and more conductor to degrade the signal, etc.,etc.
If this is indeed true, how is it scientifically possible?
Has anyone out there had any experience comparing an 8 ft. or longer version of a particular speaker cable to a 6 ft. or shorter version of the same cable?
Which was sonically superior?
In what ways?
These same sources do agree that shorter interconnects are sonically better, but they claim speaker cables should be 8 ft. or longer for best sound
Any comments or answers about this would be greatly appreciated.
Thanks.
Lanny