It's very difficult because there hasn't been any major graphic enhancements or radical new story lines to convince consumers to purchase new games.
This is from my experience in the games industry: big games prop up the big sales figures. The majority (over 70% IIRC) of sales are made after a game drops below half of its original sale price. Add the two together for long enough and you get this sort of major sales slide.
Avid gamers, think back to 2008 and 2007... I spent way too much time in front of my TV back then, because there were quality titles coming out.
In 2009 I did not buy a single game until Batman: Arkham Asylum this month. This is the first time in ever that I can remember not buying any games for the first 8 months of the year.
And the worst part is, this will get worse. Many of the most anticipated games of the holiday season have gotten pushed into Q1 2010. Q4 2009 is going to go down in history as a very, very painful quarter for game publishers.
I have a serious problem when buying games, because I worked as a reviewer so I'm used to recommending 'buy this one now, buy this one later, and just don't even think about it' and I happen to agree. There hasn't been a single game that I had to buy this year. EVE Online has been winning my interest with the new expansion, and I usually detest MMO's. The games always held my attention, but I've never been able to justify the monthly payments, yet the lack of decent games this year and the fact that their expansions add a lot to the game without costing you more (I'd never play WoW because they charge you multiple times, for buying the original game, the expansions and monthly, and it never felt fun to play).
I've heard no mention of MMO sales, but I've admittedly not paid attention to that sector. So I would be interested to see if there has been a boom or bust. Have people been cancelling subscriptions or have people switched from buying a new game every month at $70 to a low monthly fee? I may have to look it up