We're not sure how to break this to you, so we're just going to say it straight up: Super Street Fighter IV is going to have an even tougher (read: cheaper) Seth than Street Fighter IV. But we've got good news alongside that: You won't be forced to fight him over and over until you unlock that last playable character, as they'll all be unlocked right from the get go!
After Capcom's Seth Killian spoke with Kotaku earlier today regarding the unbelievably cheap final boss (can you tell we're bitter?), we shot an email to him to make sure he hadn't misspoke when he said, "Seth will be even cheaper and more irritating." Killian clarified his statement for us, saying, "[SSFIV producer Yoshinori] Ono himself promised that Seth would be even more challenging ... 'cheaper' and 'more irritating' are premature since the AI isn't finished but he isn't going to be a pushover."
When we wrote back, terrified that we'd never get to play the game's entire cast of characters, he reassured us that, "All characters are unlocked to start." We'll be getting our hands on SSFIV later this week and hopefully we'll get to find out just how much more difficult Seth is becoming.