mechanics of ECU upgrade?

i have a question about the ECU upgrade. modern cars are pretty much controlled by computers. this is pretty obvious as most operational problems on cars these days can be remedied with a reprogram or software update. the question i have is: why can't the TRAC unit be fixed with a reprogram? i would imagine that if it is overly sensitive, you should be able to fix it with a re-flash of the software. is the actual unit defective? i'm getting the two-part update next week. just curious.....