They are fundamentally the same. They may have a difference in core course here or there, but I believe the main purpose of the different degrees is to make students feel like they aren't wasting their ATAR (i.e. would you feel better if you got an ATAR of 97 and took a course with an ATAR of 95, or 81?)
also, BIT is four years whereas BCST is three years. BIT's fourth year is either an Honours year or just coursework. Once you've done BCST, you can either do Honours or take your degree and run