I don't know if I completely agree with you metaldevil, I have 9 games and quite enjoy all of them
On launch day I picked up PDZ, the day after I picked up PGR3 and Condemned. The system sellers for me were DOA4, PDZ, and PGR3. I followed all the pre-release hype for those games and it's those games that sold me the console, if none of them were coming out I probably wouldn't have bought one at launch.
Since DOA4 was delayed I got Condemned because I like Adventure Horror type games and it looked like an interesting spin on it. It quickly became one of my favorite games, though PGR3 took most of my time. A few weeks later I picked up Kameo because I really enjoyed the demo and wanted something on the console that my GF could get into and play, it reminded me of all of those great N64 adventure games. Then I got DOA4 when it was finally released.
After Christmas I picked up Tony Hawk American Wasteland because I'm just a big fan of the series (I've played through and 100%ed every TH game that's ever come out). The only reason I didn't pick it up at launch was because I wanted my first few titles to really wow me graphically, THAW looks great but it's not a WOW title in terms of graphics.
After I finished Tony Hawk I traded it in the BST for Amped 3, Again I had really liked Amped 2 on the Xbox 1. I'm a fan of both the Amped and the SSX series and while I head Amped 3 is a bit more like SSX then previous titles that sounded great to me because I like both styles.
I bought Ridge Racer 6 used from the BST, Again I was a fan of the previous titles, I actually own Ridge Racers 1-5 on the PS1 and PS2 respectivly. I like the PGR series much more then Ridge Racer which is why I didn't buy it until just last week.
Finally I also bought COD2 used from the BST. The demo was on all the kiosks in the stores and I'm not the biggest FPS fan and not big on WWII games either. I didn't pick it up at launch because the kiosk demo didn't really excite me. A few weeks ago I got my OXM demo disc in the mail. I thought I'd give the demo another go since it's such a popular game and all of my friends keep nagging me to get it and play online with them. Playing the game in my own environment, on my projector with 5.1 it was INTENSE, and I started looking for a copy that night...
I own 9 games and honestly I don't have nearly enough time to play them all, the only game I've completely finished is THAW, most of the games I have I've barely put in any time with.
I think the reason the attach rate is so good is simply because there are a lot of good launch games. Sure there isn't ONE spectacular Killer App, but I'd much rather have 9 Great games then 1 Amazing game. Variety is the spice of life. I didn't buy an Xbox 1 until a few months after launch because at launch there weren't any games that really grabbed me. With the 360 I had to be selective with what I got because there were SO MANY games I wanted and I couldn't afford to get them all at once.
I enjoy a wide variety of genres I have well over 40 Xbox 1 games in my collection right now, At the peak I had closer to 70 (I sold a bunch). My Dreamcast collection stretches into the 3 digit range. I consider myself a hardcore gamer, which why my personal attach rate is MUCH MUCH higher then that of the causal gamer.
I think the reason the attach rate is so high is simply because of the number of quality titles and well known franchises availble at launch.
Amped
Call of Duty
Dead or Alive
Final Fantasy
FIFA
Madden NFL
NBA 2K
NBA Live
NHL 2K
Need for Speed
Perfect Dark
Project Gotham Racing
Quake
Ridge Racer
Tiger Woods PGA
Tony Hawk
These are all AAA franchises that will sell based on reputation alone. Give them next gen good looks and make them all avaible within the first month of launch and you have a console with the highest launch attach rate in history.