I my guess is that what's really happening is that Apple is being paid off not to compete in search. As Google has shown, search can be incredibly lucrative. The profit motive would be pushing Apple to this end. They have a large base of loyal users that Apple Search could be be pushed out to as the default.

Google pays Apple enough not to take the risk in trying. If Apple Search was a hit it would be a threat to Google. There's always the possibility that it would be the next Bing or Apple Maps, an inferior money pit, so Apple is happy to take the cash.