Necropost but I'm stuck home and there's a heatwave outside so I'm just gonna answer this because I've researched it quite a bit and there doesn't seem to be much about biomedical engineering on forums so someone might actually find this useful/helpful.
The difference is not simply the length, you do a thesis at both USYD and UNSW.
USYD is 4yrs and has a bachelor of engineering dedicated to biomedical engineering. It consists of a mix of mechanical, electrical, mechatronic engineering units and basic sciences and physiology. The problem with this degree IMO is that it doesn't prepare you for any specific engineering field. Biomedical engineering is a term that encompasses ME, EE, SENG, ChemE, Mechatronic Engineering that is applied to the medical field meaning employers will usually look for someone that has a degree in one of these disciplines and either a postgraduate qualification in biomedical engineering or relevant work experience within the field of biomedical engineering. Another thing to consider is that there aren't many biomedical engineering jobs in Australia so it's a safer investment to complete a more traditional engineering degree along with a postgraduate qualification in biomedical if that's what you're interested in. Which brings me to UNSW.
UNSW has a 5 yr combined B Engineering/Master of Biomedical Engineering degree that lets you pick from ME/EE/ChemE/SENG/Mechatronic/TELCO/Bioinformatics and combine it with a masters in biomedical where you do postgraduate level courses in physiology as well as actual biomedical applications of engineering and you do a thesis that is relevant to your both your engineering major and biomedical engineering.
Having said all this, the UNSW degree seems a lot more challenging and having access to postgraduate work while still an undergrad can give you the chance to work with some amazing research teams like the Bionic Eye team. I know there was a student from UNSW that went on to do a PhD in Biomedical Engineering at MIT after going there for a study abroad session to work on MRI's.