It might be a similar effect but it's not the same effect. There's a definite difference between wanting to say that you are making the effort to take part in the electoral process but that you don't want to lend your support to any of the candidates; and for whatever reason not correctly filling out the ballot paper. If nothing else it makes for a much more interesting statistic, spoiled ballot papers tell you nothing about the intent of the voter, a 'none of the above' option would help with that.