Short answer: Yes, it’s probably is. Mainly because of the massive hash rate. However the system configuration might be same as other pool such as Btcguild.com. People reported that they have better hash rate on btcguild.com but not making as much due to various factors such as luck and fees.
No doubt Ghash.io has been the dominant pool on Bitcoin mining (SHA256), and also with Scrypt mining also. Currently Scrypt on ghash.io is about 10GH/s, while other pools are much smaller.
Gash.io appears to have private mining farm. Meaning that a great percentage of their hash rate came from their own mining hardware. In other word, ghash.io have a data center that have a lot of mining hardware hook up. In addition they’re making more money off of public miners. However ghash.io have no fees, that is just amazing, but they do have transactions fee, such as the fee for withdrawing Bitcoin, but very small fee. While other pools have at least 1-3% fees.