I'm not entirely sure which way to direct blame. If I recall correctly didn't similar problems happen to the Bioshock 2 dlc and game, except 2k or whoever is was, gave the dlc for free to everyone who owned the game at the time and converted dlc to steam so that new folks could purchase it.
Similarly, didn't a similar thing happen to the Batman games, and they gave everyone the game of the year editions for free (ie with dlc) even if they didn't own it, and again put the dlc back on steam for new people to buy.
Is any of the SFIV dlc coming back to steam? That might hold the answer. If it is back, then you could argue that Capcom is indeed, being a dick about it. Hopefully if the community make enough noise, it may get fixed somehow. Frankly though, I don't know the logistics of doing such a change or the financial implications or the rights that licences grant users in such a situation