I think given that buying a bat is not really something one can 'try before you buy' aesthetics play a major part in the decision.
There is a perception that clean straight grains equal good willow/ playing properties but in reality I, as I'm sure many others, have had bats which are not aesthetically pleasing but play really well.
I was just thinking the other day that all my bats of late have been bought at arms length (online, etc) rather than going into a shop and getting a feel for the bat/ tapping it up. As a result I have had some lovely looking bats that I just haven't gotten on with.