Hearthfire is the second 360 exclusive DLC. Which means all future DLC should be day and date on all platforms, which of course is impossible if the PS3 version is so badly made that it can't support DLC.
My theory, which has since become the general consensus around here, is that Bethesda realised months ago that the PS3 version of Skyrim was so bad it would never support DLC and so stopped working on it in order to create Hearthfire and whatever the next DLC will be. For the last three months they have merely been stalling for time until Dishonoured ships so that there isn't a mass cancellation of pre-orders. Once that game has shipped and Bethesda has been paid by the retailers, they'll come clean and announce that they're "tried for months, but nothing works, DLC for the PS3 is now officially off the table" - there'll be a massive backlash of course, but they'll ignore it and eventually people will just walk away.