For the Australian case, there are indications of a number of people, indeed, casting votes simply by ordering them from the top down on the list. There are always going to be a number of those votes in any kind of system. The easier your system is, the less of those kinds of votes you're going to get. If you think of a proportional system just causing a list vote, then there's not going to be such an effect of that.
Furthermore, if you have a “none of the above” option, those who really don't care have that option, and would either cast an invalid or a blank ballot or just make something up.