Come to think of it, you already get download-able content.
You get maps that people created! xD
But seriously, even if there WAS download-able content for brawl, or any game, they'd have to be small, and uneffective to the gameplay.
If they charged for you to download things, and they released...I dunno, a character for a certain amount of points, the person who is fighting someone who has that character, can't play because he never has any Wii points.
Get what I'm saying? If it was a single player only game, then sure would be great to have DC. Or, making a Single Player game Multiplayer by downloading the upgrade. They've done that to Killzone liberation for the PSP.

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