Season One, Eviction One, and an interesting character was the first to be evicted. Start as you mean to go on, I guess. The flaw in the format was immediately apparent.
The supposed flaw, but also actually one of the shows great drivers. In attempts to fix that issue (blatantly in some cases) in some later efforts, probably more so in the UK than Australia), it became clear that keeping the dominant "interesting" characters around usually meant rather boring uneventful evictions, and then quieter characters leaving really didn't shake up the house from week to week in the way big characters leaving would.
Big Brother is always at it's strongest when it plays out naturally - even if along the way it may seem like that.