I am tired of all these conspiracy theories. If it was just an unlock code, then 1.86 MB is a pretty dang big string of characters.
The fact of the matter is, there are no new assets in this DLC. There are no new graphics, sounds, levels, etc. It uses the game engine that *shock of all shocks* already exists on the disc because it is the game! The VS mode is just new code that adds functionality to the game engine. Hence, it is small in size.
Seriously, people just believe whatever FUD they read, and don't bother to think/research for themselves. It is a scary recurrence in today's society when the uninformed masses get all whipped into a furor and grab their pitchforks...
What PROOF is there that everything is already on the disc and the DLC is just an "unlock code?" Right...there is no proof, just speculation because the DLC is so small.
/facepalm
The only good thing that might come out of all this ignorance is maybe Capcom will feel the pressure from the masses wielding their pitchforks and offer the DLC for free as an "act of good will."