It is not just the acceleration that is the issue, the braking performance of the BMW is very poor in comparison to the S4. 131 feet versus 108 to stop from 60? That is a rather large difference.
Handling performance also was in the S4's favor pulling .91g's and a 25.6 seconds around their figure 8. The 335i took 26.7 seconds around the figure 8 managing .86g's. The all seasons no doubt hurt it a bit but this does not change the fact the Audi crushed it here by over a second.
It isn't even the performance necessarily but the steering is muted on the 3 Series, it is more expensive than the Audi, gets worse fuel economy, and the electronics get in the way. MotorTrend says this is odd and to us it is almost like the twilight zone.
BMW is falling off whether fans want to admit it or not. The new 328i raised the bar on the low end but in the mid-range of the lineup BMW is not innovating in the way they did when the 335i was first introduced. Perhaps the way to look at it is simply that Audi is getting much better. We wish BMW would get out of their slump already since changing over to the turbo motors. Clearly some of the magic is gone. The question is, will they get it back?