Sega's "Game Contents" division (i.e. home video games) was down 5.1% for the nine-month period ending December 31, with the company reporting 63.5 billion yen ($833 million) in net game sales from the division ... and 5.5 billion yen in total losses. As for reasoning, Sega said only that "in the overseas markets, sales of the new titles remained slow as affected by adverse market condition." Best we can tell, that "adverse market condition" refers to our economies all being really, really terrible.
The publisher shared sales numbers for its major releases. Sonic Generations sold 1.63 million copies across four platforms (Wii, PS3, PC, and the 3DS Generations game). Mario & Sonic at the London 2012 Olympic Games outsold it with 2.39 million copies -- despite not being released in Japan yet, and only being on one platform at the time, the Wii. And, uh, despite being a Mario & Sonic Olympics minigame collection. Hatsune Miku Project Diva Extend for PSP (released in Japan only) was the other named hit, with 290,000 copies.
Looking up at Sega's sales by platform, it's worth noting that Sega's single PlayStation Vita release, Virtua Tennis 4 (called Power Smash 4 in Japan) sold just 10,000 copies between the Vita launch date of December 17 and the end of the year. That ... doesn't seem very good.