[Ghoulish Delight]

Most likely some weird quirk with Google's database where the stored data for the distances along the exit ramp calculates out to a preferred route based on whatever algorithm they're using than the doing the calculations with the stored data for that stretch of freeway.

Computerized mapping and route-calculation is an inexact science and one that requires a lot of clever programming shortcuts to execute efficiently. If you want to get bored go look up the computer science topics of "NP complete" and "traveling salesman". The short version is, any computer program that is able to give you a 100% guaranteed shortest route calculation will require an exponentially increasing amount of time to execute as the amount of possible routes increases. So with the huge amount of data that a nav system has to process, guaranteed accuracy is sacrificed for speed, leaving the possibility for weird inaccuracies. I imagine they also try to cover for some of that by doing a lot of re-calculation on smaller portions of the route as you go, which is why you wouldn't see it in the initial route but it might show up en-route.