Officially Dawnguard is exclusive to Xbox 360 but fans fully expect it will migrate to PS3 soon enough, having already done so for PC. Bethesda clarify Hearthfire is a "separate" parallel project.
Fans posed questions to Bethesda marketing big wig Peter Hines, who replied they are "working on multiple projects, even beyond those two things."
"But is it going to be delayed because of Hearthfire being in development?" asked one fan. "No, they are separate things," replied Hines. Bethesda is yet to offer a window for when Dawnguard would appear via PSN. "We are working on multiple projects, even beyond those two things. The entire team doesn't work on one thing at a time."
"We have not announced Dawnguard for any other platform, nor given a timeline for any such news," he said last month.
"If we have news, I promise I'd tell you." The intended 1.7 update for PS3 Skyrim will include all the new features and fixes that Xbox 360 and PC's 1.6 has enjoyed which includes mounted combat. That's something at least. Hearthfire will be arriving on Xbox 360 first, September 4th, with a PC and PS3 release speculated a month later.