It's not the first time this has happened, indeed it's pretty usual. These are some of the games that didn't get DLC on PC:
Divinity 2: Ego Draconis (Might as well get the "But European devs don't do this!" squished first)
Need for Speed: Whatever
Saints Row 2
Racedriver GRID
BioShock 2 (Partial DLC coverage at the moment)
FarCry 2 (The Fortune('s?) pack was around, but it disappeared quickly; It is possible to get it as part of a FarCry 2 release but not on its own anymore)
It's not just EA, it's 2K, Codemasters, THQ - They're all doing it. You could probably find more, especially GfWL titles, by comparing them to their 360 counterparts, but that's just a small selection above. Missing out on DLC is not something that's unheard of, and I suppose we just have to... deal with it.
I think the distribution of DLC can be a bit of a pain for some devs, though. Direct2Drive is one of the few places they can do it without hitting some form of barrier - I think Impulse requires Impulse-registered games for DLC, and Steam certainly does - So that leaves them with D2D, publisher/developer website (Not all of which have stores, remember) and possibly GamersGate. What's the point if they can't get the message across that it's out there? 2K released DLC packs for Borderlands on disc, SEGA released them for Empire: Total War (I think?), but if they don't have a lot of DLC then what's the point?