Since it is highly likely that Super Street Fighter IV will add new characters to the roster via download, we need to take a look at BlazBlue: Continuum Shift.
Even if you don't like BlazBlue, there is a very interesting development taking place with that game that you should know about. The game currently offers additional playable, downloadable characters. Currently, only one is available, though there are plans for at least two more, including Valkenhayn, pictured above.
The dynamics of adding characters to a fighting game via a download are very involved. First, there's the cost issue. The first character added to BlazBlue costs $7. Let me repeat that: $7 for a single additional character. While the cost of the upcoming characters has not been revealed, it is assumed that it will remain the same. Whether what you get is worth $7 or not is your decision to make, but that is no small investment relative to a $40 full game. Some would argue that an entire character is worthwhile, since people pay more for costumes in SF4 that serve no gameplay purpose (and are on the disc already, unlike the BlazBlue characters).
There's also the issue of being able to play as the character you purchased against people who did not make the purchase. BlazBlue accomplishes this by patching the entire game for all users. The data for the new character is installed into every player's game: paying customers can fight as the new character, while other players can only fight against it when challenging those paying customers. If you have not paid for the character, you cannot access it, even in training mode. The only way to get match-up experience against a DLC character is to fight someone who has paid for it or to buy it yourself.
This puts a burden on the players and tournament organizers. If you take issue with showing up to play SSF4 only to find that your favorite costume is not available, imagine your entire character not being available. Tournaments will have to be run with consoles that have purchased the DLC at a cost of $7 per character. This could get expensive for tournament organizers.
We need to watch this situation closely. Will $7 remain the de facto price for a downloadable character? Are different characters worth different amounts, based on their tier status? Should the cost vary with how intricately designed a character model is or how difficult the character's moveset is to program? Would you pay $7 for Hugo? How about Elena?