Yes, Uber expects 5 to be the norm. Most regular passengers understand that by now and rate all drivers 5 if they get them there.
Since I stopped driving, Uber has made some changes that I'm not that familiar with. For one thing, Uberpool ratings were inherently lower, because a passenger could have an issue with a co-passenger or the route, and downrate the ride for reasons beyond the driver's control, so I think they ask the reason for the rating and don't count it if it's a non-driver issue.
Admittedly I have a driver perspective, but I say feel pity on the driver and give them a 5 rating almost regardless. A recent study showed that Uber drivers net $3.37 an hour after expenses. I don't doubt that for a second.