Since everyone else is tossing in two cents...
PlayStation 2's launch, both US and Japan, sold almost entirely on a "just wait" philosophy. Granted, I enjoyed PS2's launch (SSX, Tekken Tag, RRV, Swing Away Golf
), but there wasn't a huge MUST HAVE for it. It was all about waiting for Final Fantasy X, Metal Gear Solid 2, Gran Turismo 3, Resident Evil 4 (at the time), etc. The other big seller, obviously, was the popularity of PSone. Name brand familiarity and trust. Sure, it's main competition was the Dreamcast, but back in 1999 that seemed pretty significant. SEGA seemed ready to make a huge comeback- early next gen system launch, tempting launch titles, online capabilities, a new Resident Evil on the way, etc.
I won't make the mistake of comparing Dreamcast to X360, but even prior to launching PS2 the gaming world was aware of Nintendo's GameCube and MS's X-Box. PS2 had the 'wait' scenario working as Dreamcast came out, then the 'why wait' (for NGC & Xbox) once it was finally released.
Why does PS3 have to be any different? Strong series brands back in 2000, such as FF and MGS, are still very strong today. How many of you will be buying PS3 next year for games like FFXIII and MGS4, which may or may not hit as soon as 2007 or as late as 2008? I can safely say that I will, but this next gen I can add other series to the list, like Devil May Cry, Silent Hill, GTA, possibly a sequel to God of War, a new Jak, new project by ICO/Wanda's Ueda, etc.
I don't think it's too ridiculous to believe there are a lot of gamers like myself that will get a PS3 right off the bat simply for the guaranteed prospects of established, quality brands- multi-platformed (i.e. Ridge Racer) or not. Hell, it took almost a whole year of PS2 before the games I was really interested in started coming out (like SH2, FFX, MGS2)- but there were still some great games that tied me over, like Shadow of Destiny, ZOE, Twisted Metal Black, Dark Cloud, just to name a few.
X360 will most likely do pretty well this gen, but as long as Sony secures the games/series that the PS2 userbaser enjoys, it would take a monumental fuck-up to lose any significant ground, I think.
Personally, as I've said before, I hope X360 and PS3 are both very strong. Healthy competition within the market would, hopefully, inspire developers/designers to work harder. Maybe the nostalgic fool in me just wants another Genesis/SNES type era.