I doubt it. All people I know use Google as their URL entry field, as the concept of URL is too machine-oriented to be comfortably used by the average guy, when good search is available. Given that, Google donating to Wikipedia is a pure win-win situation.
Crome's omnibox search also takes users to wikipedia without visiting google. They could show ads in the omnibox, but the space and user experience is more limited.
And don't forget that most sites don't get all their referrers from Google, so users are getting there via another way. Some of those are indeed direct traffic, without an intermediary.
It may not really save to much time, but if a tech guy like myself does it that way, average internet users would probably be even more inclined to.