GPS are accurate if you are in open sea with several satellites in the horizon. GPS are not accurate with tall buildings and with cloudy skys. Garmin recommends users to take similar readings over the course of several days to get location spot on.
To see GPS accuracy isues with your smartphones, there are many mobile apps that create a track log of your movements, some at 1 seconds intervals. If you upload to Google Earth you will find lots of overlapping lines. If you sit at a single outdoor spot for 1 hour, you will find birdnest patterns as your location fix drift about.
The satellite images you see of Googlemaps are obtained from 3rd parties. There are overlapping issues which results in offset errors of as much as 15 meters inaccuracy.
Next Googlemaps has to interpret what we type in the search bar to get us the right location. You can type any text and Google will find you the address. Just don't expect Google to figure it right. One useful googlemaps feature is searching for location using postcode.
But as more and more companies sign up to display their location on Googlemaps, I expect even more errors in the near future. Many from people who use cheap GPS equiped smartphones or worst, people who cannot read maps at all to provide Google with their location data.
These problems should sort themselves of. Meanwhile, enjoy Googlemaps. Its free and full of goodies, although many features are not available in crippled smartphones.