Because BMW now shares many electronic components accross their entire line-up. The 5 & 6 share exactly the same electronics. And the 3 & 1 series gets their electronics with slight changes.

This means (at least on the electronics front) that problems get worked out much sooner as the same testing schedule which was previously used to work on 5-6 different electrical systems now is spent working on one central system.

Also the iDrive based BMW's are easily updated. New releases of the software are quite common. Since new tech starts at the top and trickles down. So the E70 will have a lot of gremlins already worked out. The 3's are also very good in the electronics front.

BMW also has good cashflow. If you remember back into the late 90's with the E53 was being developed, BMW had to cut costs with the rover debacle. As a result, the testing phase of the E53 and other cars was compromised significantly = lower quality.

Not only this, but Panke has said repeatedly that BMW's new long-term goal is quality, quality, quality...