google actually uses cell phone towers as an additional input, triangulating your position by noting the tower (or wifi hotspot) you're access maps from. apple relies exclusively on GPS.
Because they are greedy assholes. Instead of utilizing mapping technology companies that have been around for decades (like Nokia's NAVTEQ) they are starting from scratch on their own to increase profits and screw customers in the process. They are a software company trying to provide maps rather than a map company providing maps via software.
http://blog.crowdflower.com/2012/12/the-accuracy-of-apple-maps-listings-reality-check/ Will I get where I want to go? So when you search for a business, what are the chances that you’ll find the business you want AND the address will be accurate? With Apple maps you have a 71% shot, compared to 88% for Google Maps and 78% for Bing. But with a 3.4% error rate, you’re three times as likely to be sent on a wild goose chase with Apple Maps. In the UK, the situation is dicier: you’ll get a good listing 33% for Apple Maps, compared to 88% for Google Maps and 55% for Bing. And 30% of the time, you’ll get a listing, but it’ll be incorrect.