The cable tang in our Laredo and Natchez Bowie knives is used primarily as a shock distributor. The cable acts almost like a guitar string and sends shock out the end of the pommel, rather than into the handle and subsequintly the hand. This promotes longer life in the handle, and makes it less likely that the user will take shock directly into his hand, allowing him to maintain a more secure grip. Since these are primarily designed as fighting bowies, a secure grip is extrelemy important. If you have watched Lynn's video on using the bowie's handguard for defense, then you can see how much shock this knife may take in a combat situation.
It also makes the knife a little blade heavy, which moves the "sweet spot" of the knife further fvorward and gives it greater impact.
Manufacturing the knife with the cable tang is a more expensive process than simply making the knife with a full tang, so this is done with intent and design. It is definately not a cost-saving effort. We have never seen a cable tang break under normal usage.