Ratings and demos are different.
The CW cares more about demos (which for the CW, the most important is the 18-49 female demographics.)
The reason GG keeps getting renewed is it's demo's, not it's ratings.
So, for demo's, it goes like this generally week to week:
TVD: 2.0
GG: 1.8
90210: 1.5
OTH: 1.3
Nikita: 1.2
Hellcats: 1.0
I don't even technically look at the overall ratings for shows because they don't really count much. It's all in the demos... which Hellcats is the lowest rated in regards to that dept on the CW now. It's why GG and 90210 and other shows get renewed time and time again with such low average ratings....the demo they provide for the CW is HIGH.