I agree that urban crews have a lot more practice than rural ones. On the other hand, my station in a large metropolitan area of Virginia got a severe (and well deserved) talking-to from a new member who had moved there from near where I live now (boonies of southwest Virginia). He was appalled that we weren't constantly checking vital signs. We had gotten sloppy, because we were seldom more than five minutes from the nearest hospital. He pointed out that where he ran rescue, it could easily be 45 minutes to an hour to the nearest ER, and that not all of them were staffed 24/7. A patient's life was dependent on the skill and attention of the ambulance crew for far longer than in an urban environment, and they knew they had to keep those skills current.
Regarding the difference in skills between crew members, I'm familiar with only one urban and two rural systems, but in all of those, the least trained person was also the least likely to be driving. He or she was in the back with whoever was in charge on that call, so they could be further trained. Perhaps some places just don't have enough people to make that possible, but I never went out with fewer than a three-person crew.