It's miniing vs. mining with upgrading. If you did the same analysis with in situ, the extraction rate of return would be higher, so the gap would be larger. There is only a single in situ facility (Long Lake) which is integrated (i.e. with an upgrader), and Suncor processes a significant amount of its MacKay River in situ bitumen at its upgrader near McMurray as well.
Overall ratio looking ahead is far more in situ than mining.