I agree to an extent, though I have two issues with what you say:
1. Netflix sold a significant amount of 360s in 2008.
We've discussed this before, and I still feel you have little evidence that this is the case. Netflix was already available on a variety of platforms at the time, and at that time the 360 had just dropped to $199/299. I'm pretty sure any such gains in hardware sales during that period would be more attributable to the latter than the former.
2. It is rare that one title actually sells somebody a system. What sells systems is the breadth of an entire library, though individual games can be the incentive to finally get somebody interested in a console to buy in.
I can guarantee you the PS3 would still be a distant third if it were not for Sony's first party efforts helping to differentiate the console from the 360, yet looking at individual titles, only a handful have caused a noticeable spike in system sales around launch, like Uncharted 2 and Killzone 2. If you were to remove the weaker/filler titles - Infamous, MotorStorm, and others - while keeping just those games that had a clearly discernable impact on sales, Sony's library would be considerably weaker for it. The console would not be doing as well as it is today, nor would SCEWWS have near as many fans as it has now (both of which go hand in hand, I'd say).
Just look at the high number of multiplatform owners this generation (as shown by how far multiplatform sales can swing based on factors like additional content for one version vs another). People wouldn't be buying PS3s in addition to 360s if not for that exclusive library.
And of course, there are long term benefits to be found through franchise/brand loyalty. Much like the Mario/Zelda/Metroid fans that stick with Nintendo through thick and thin, Sony has made many new fans thanks to its diverse software efforts this generation. Microsoft relying more on third parties could set them up for a situation similar to Sony earlier this generation, who got screwed when every third party started ignoring them in favor of 360. You can't rely on third party franchises long term, and for this reason Sony lost many of the "fans" that were really only interested in their platform because of GTA/DMC/FF.