Wow, this rating system is interesting.
I just fought this rank #3 Silver Zerg player that seemed like he should have been in Copper. He never even attempted to expand and just tried to sit in his base and tech to air. I scanned him earlier and saw him getting air, so on his first attack on my base he only killed 1 SCV because I had marines and vikings ready. He then still sits inside his base and proceeds to produce more of the exact same units.
By now I have complete map control (and an expo) and he's pretty much lost, yet he's still inside of his base cranking away at those air units. No scouting, no attempt at an expo, and completely tunnel visioned.
I know this is still the beta and this is not completely representative of all silver players but he has nearly 200 games so you'd think by now his rating would be reasonably accurate.