Is Toyota's Accelerator Problem Caused by Embedded Software Bugs?

http://www.embeddedgurus.net/barr-code/2010/01/is-toyotas-accelerator-problem-caused.html

However, at least one article I read yesterday suggested that one fix being worked on is a software interlock to ensure that if both the brake and the gas pedal are depressed, the brake will override the accelerator. On the one hand, that seems to mean that software is already in the middle; on the other, I would be extremely surprised to learn that such an interlock wasn't already present in a drive-by-wire system.