I wouldn't put the Defender in the same category as the Tank, Survivor or Seidio Rugged. In fact I'd put the Defender in a category between the Speck Candyshell an the Tank, Survivor and Seidio Rugged etc.
Why? Because the Defender doesn't offer as much protection as the like of the Tank. And most importantly the Defender offers much more style than the likes of the Tank for the Defender being a semi rugged case. Such as showing the Apple logo cutout, not much thicker than a Speck Candyshell, just shows the glory of the iPhone better than the likes of the Tank.