Laser trimmed resistors on the same substrate tend to have similar tempco and aging. While aging can change initial resistance it is very likely to do it in similar fashion (same material) to all resistors keeping division ratios pretty much the same. In addition, the largest changes in any resistor are just right after production. Older resistors change very little. There is an assumption that non Delta-Sigma DACs are R2R - not necessarily so and many of them have self calibration mechanism. Mentioned Philips TDA1541 is R2R but only for the 10 highest bits while lower 6 bits are controlled by Dynamic Element Matching (DEM), based on emitter scaling 10-bit current divider. It is possible to have resistor ladder, current scaling, voltage scaling and charge (on capacitor ladder) based DACs plus combination of them in multi-bit converter.
Even if we forget technical reasoning - IMHO only insane company would design a chip that shows sound deterioration after 10, or even 20 years.
