BeefJack writes, "If, like the majority of us, you've noticed Street Fighter IV's boss character, Seth, to be painfully tough despite the difficulty setting, then there may be an explanation - and a fix - for this seemingly stupid imbalance..."
Update
BeefJack would like to point out that if you read the entire article you will find that the bug only seems to apply to the PS3 version of Street Fighter IV.
If you experience no issues you are likely playing on the Xbox 360. The article was not written to debate the overall difficulty of Seth but to propose that a bug has prevented him from scaling in difficulty correctly.