Bing provides API access to its search index. IIRC the type of queries you can do are a bit more sophisticated than just "what's available via the Bing search engine" (e.g. select a market).
That's not index access. You are getting ranked results. Index access would give you the posting list for the term "moose", or the intersection of the posting lists of "moose" and "caribou", or whatever.
You can't make a neutral service that returns ranked results, because that's contradictory.
You can't make a neutral service that returns ranked results, because that's contradictory.