Cody's theme in SSFIV is heavily based off of the intro from Final Fight. The rapper repeats the words "Turn the beat back!" quite often. This is a look into Cody'spsyche; he longs to relive his glory days as a hero and get out of his funk, but sadly has convinced himself that things can never go back to how they were.
Near the end, the song gets rather uplifting and whimsical...until it loops and goes back to being a gritty rap. More than likely, it's Cody remembering his time as a hero, only to go back to his current, uncaring self.
Kinda doesn't work anymore now that Makoto has risen quite high in the tier lists thanks to the buffs she got in Arcade edition and Arcade edition 2012.
One aspect of the US marketing was slapping on surnames to some characters, and Ryu became Ryu Hoshi. Factor in the Japanese name order, and it ought to be Hoshi Ryu. And 'hoshi' means 'star' so the full name in kanji can also be read as Seiryu - one of The Four Gods.
Couple this with the fact that his stage in every iteration of Street Fighter II is the Suzaku Castle and you can see a motif coming. Where Byakko and Genbu come in is something else (though Byakko can be argued to be Sagat, considering his own "tiger" motif, and Ryu apparently takes more self-improvement from his rivalry with him than from the one with Ken).
Dan is significantly less wimpy in Street Fighter IV than in previous appearances. You might think this is because the developers are just trying to make him more fun to play but think about what Dan has been doing for the past three years. He's been hanging around with Blanka and Sakura. Even if he is getting his butt kicked regularly, practice with both fighters is bound to improve his fighting style.
Juri hates Shadaloo for killing her parents and maiming her. S.I.N. is stated to have been Shadaloo's weapons division. In her Story Mode, Juri joins S.I.N. and works for its leader, Seth. Is it that she has/had no clue of the link between Shadaloo and S.I.N.? Well, if you examine her ending, it can very easily be a case of her playing the role of The Chessmaster, playing both sides against each other to make the whole organization destroy itself from within—that would be her ultimate revenge!
Seth's was named after former Capcom employee Seth Killian and is also derived from the Biblical Seth (Being that Street Fighter's Seth replaced Abel as Shadaloo's main experimental subject after the latter fled). Seth's name also coincidentally could have a third interesting level of meaning in referencing the Egyptian god Set (also known as Seth), which fits with his desire to become a god-like being.
Why does Dan's Japanese voice sounds so husky and gritty in SFIV and its subsequent sequels? Well, since Osamu Hosoi voiced him from the Alpha series up until he was replaced by Toshikyuki Kusuda, it could be a sign that constantly screaming "OYAJI!!!" for years eventually took a toll on Dan's vocal chords.
In Street Fighter IV, whenever a Shoryuken is performed, it has a certain "tail" following it, either dark black like ink, transparent like air, flaming, or white. These all correspond to the force used by the person performing the Shoryuken. Ryu, Akuma, Evil Ryu, and Oni's Shoryukens all have an ink-black tail because they use the Satsui no Hado in various quantities to power it. Ken's Shoryuken is flaming because Ken is channeling his aggression into it. Gouken's Shoryuken is pure white because he uses Mu no Hado, and Seth's Shoryuken has a transparent tail because it is "empty", and isn't using Mu no Hado or Satsui no Hado.
The reason that Dan is still incredibly weak compared to the other fighters is because, according to Gouken, he refuses to let go of his resentment for Sagat killing his father Go Hibiki. At first it might not seem like this would make much of a difference, until you remember that Sagat wasn't very strong himself (Gen didn't see him as worth his time) until he let go of his resentment for Ryu scarring him in the original World Warrior tournament and they became friends in Alpha. Now Sagat is so powerful that Oni considers him a Worthy Opponent. Makes you wonder what Dan could be like if he could let his anger go.