I am actually a strong proponent of pixel perfect implementation myself from design -> production.
I think the one aspect you missing in it’s entirety is the relationship between development and design (similar to the way that copy & design had similar struggles in the 70's).
If you incorporate the developers/engineers early on with the designers and vice versa, with lots of communication the designs and implementation would reflect one another. This would be due to feedback in the design process early on from engineering, and design would be involved with the implementation phase.
The longer that relationship is nurtured, the more coherent the process and implementations will be.
With the fragmentation of these relationships, design often sits in a ivory tower, and complaints of poor implementation are commonplace. Pissing off engineering, leaving every unsatisfied.