I've made the same observations. One would think that all of these map programs access the same satellite imagery, but apparently not. Part of the fun is trying to estimate when some of these photos were taken. Because they are all "snapshots in time", another interesting thing that I have noticed, but of course, I'm likely stating the obvious, is that as you zoom in, you zoom so far, then the photo switches to a new shot, sometimes taken at a different time. Occasionally, things disappear because the next photo accessed is all of a sudden, older than the last one.