Yeah it probably is down to money rather that some programming/coding limit
But I very much doubt that microsoft pays google to have Bing as an option for default search in chrome. Google probably loses out when someone makes bing the default. But rather than restrict it they allow you to use bing if you want.
Also there is the fact that there is no way that wikipedia pays opera anything so if opera can have wikipedia as an option they should have kept bing. Or at least made it a lot easier to add bing ourselves without having to edit .json files or whatever else needs editing