From my own observations, Mainly five types of people do BEc:
1. People who didn't get the Comm UAI, and got into Eco in order to attempt transfer.
2. People who take their economics seriously and professionally, and want to attain a fully professional - especially maths (metrics) oriented degree to get into places like the RBA.
3. A rare group of people who want a more tradional approach to their business degree, and usually study diverse subjects within the field of economics specifically.
4. People in combined degrees, especially law, who wish to do it over Comm for reasons 2 or 3.
5. People who enrolled for number 1 but decided to stick with BEc after they found out in first year that an economics major is probably the best compliment to any other specialization.
I know a few people who do Eco even though they could've made Comm, heck I'm mainly doing it for reason 3, and to compliment my politics major, and while the marks of people in group 1 would probably be lower, I have the general perception that marks for people in those other 4 groups are average+ , if my own marks are of any indication.