i'll never understand why people insits on paying $10k more for a nissan with leather interior.
Well, for the same reason that people pay 10K more for an Acura that's actually a Honda with leather, and for a Lexus, that's actually a Toyota with leather. It's a premium brand. And while BMW and other Germans take the unequivocal lead on performance and handling, their 'premium-only' status keeps them from selling huge volumes of great, reliable cars en masse because they are far from the price points of many buyers. Japanese automakers don't have the same problem, as they have vehicles that meet almost every price point.
In terms of the comparo between the G37 and the 335i, yes, you can read car and driver, or edmunds, or any of the auto rags, and they'll all tell you that the BMW wins by a small margin (~2.3 points on a scale of 100). Not some slamdown, in- your-face, shutout of a victory. Naturally the BMW is faster - it's got a dual-turbo, with a completely different power delivery band, different torque curves and is also lighter than the G37.
However, the G37 was also named by car and driver as one of the "Five Most Significant Debuts of the NY Auto Show". And the G35 sedan comes closer to beating out the 328i sedan every year in each of those mags. Does that make it a better car, no. But it's a pretty great car given the price. Obviously, if price isn't important, you buy the BMW. But for $41,000 starting price, you think they'd include something other than "leatherette" on the 335i.
For people who are price sensitive, the Infiniti is a great option, that is about $10,000 less than the BMW, when comparably equipped. That's substantial when you consider it's about a 33% price premium for not much more of a car.