I know about some of the other tricks Google use to collect location: I've been deep through Google settings to turn them off. But they have always collected more when wireless location is on (not that I'd put it past them changing policies without making it public, this is Google after all, but they've always used the wireless for this because if you are going to poll regularity it uses less power).
The two modes don't do the same: "high accuracy" uses mobile and wifi signals in addition to GPS. It offers advantages if you want to be located inside buildings where there's no GPS signal, but where you have a view of the sky it does not improve accuracy (wireless location is an order of magnitude less accurate, so the combination is utterly dominated by GPS).