Don't condone this in any way, clearly it's an attempt to game the system to a certain extent.
However, 2Degrees in this instance are simply unlucky they were caught out (or reported by someone) - you'd have to be naive to expect that other ISPs aren't doing this if they can somehow identify volunteers (which through various means is probably quite easy to do).
My opinion is that this is probably pretty common amongst ISPs and 2Degrees were simply caught out.
I would just like to utterly refute any suggestion that Spark has ever, or will ever attempt to game the Samknows results. If you are a Samknows volunteer on the Spark network your connection gets treated no differently to any other Spark customer. I.e. you will get the same great Spark network performance whether you Samknows volunteer or not.