I wouldn't characterize myself as a worshipper of the "Magenta Line", and am fully aware of the mapshift phenomenon. However, in the 737-800, the cockpit design trend seems to moving away from reliance on ground based Nav-Aids for updating.
This aircraft has dual GPS updating, and the observed accuracy is head-and-shoulders above the 757 & 767. It's certified for Approach Navigation, unlike the 757/767. I've seen for myself the incredible accuracy of an LNAV/VNAV engaged approach down to 50 feet. Over the numbers every time! On a lucky day, the 757/767 might get within 300 feet of centerline.
So there is a distinction to be made between the various EFIS/NAV systems. Consider this....in some 3rd world carribien backwater like Haiti, where Nav-Aid inaccuracies is not surprising, all things being equal..."In Boeing/GPS I trust". That being said, the GIGO Principle is still alive-and-well on NG Boeings. If you observe conflicting information, climb and investigate further. My bet is the human screwed up machine, and not the other way around.