Once it finally recognised me I too was surprised to get a rather low score (in the middle of the "Good" band). So I ordered a copy of my credit record from Veda just to see. There wasn't anything obvious in there that I could identify as the cause of the low score, although of course they don't make the score calculation method public.
One interesting thing I did discover from my credit report however was that for the 12-15 months or so that I held a Woolworths Mastercard, and a David Jones Amex, both companies (HSBC & Amex) were pinging my credit report on a monthly basis as a "routine credit check". I don't know for sure but I suspect that those checks actually contributed to the lower than expected score. The pings stopped soon after I closed both those cards.