TechCrunch read Apple's letter to a congressman about the kind of data it collects more carefully than most: The letter says Apple dropped Google (which was, I believe, supplying cellular tower triangulation information) and Skyhook Wireless from iOS 4, which powers the iPhone 4 and 2008 and 2009 models of iPhone and iPod touch.
Long-time readers of this site know that Skyhook Wireless has spent many years driving the streets of major cities and aggregating information provided in the form of queries from mobile devices to build a comprehensive and constantly updated Wi-Fi positioning system. While Wi-Fi isn't precise, it's not far off from GPS in urban areas.
As more mobile devices gain full-featured GPS chips and functions, Wi-Fi positioning remains important as a component in Assisted GPS (which allows a GPS to get a fix faster) and in providing an initial rapid location assessment, sometimes in a few seconds.
But location data is incredibly valuable, and owning the data is perhaps worth the price. Apple has apparently, quietly generated its own Wi-Fi and cell tower databases. It has enough mobile devices in the field with GPS receivers that it can use that information to build a comprehensive picture of most cities, I'd imagine. Every time a device queries location and sends a Wi-Fi and cell environmental scan with or without GPS coordinates, that's more data to crunch.
I thought Skyhook Wireless would have a leg up here because of Google's agreement to not scan for Wi-Fi in several countries (or perhaps worldwide) after it's data-collection debacle with Street View. And Apple's not the only fish in the pond. Skyhook has deals with many, many other platforms and providers.