As I recall, the earlier buses had rows of seats with a NARROW aisle in-between - wide enough for only one person to stand. Those cattle cars they use now may move more people at a time, but they aren't making guests happy, which in time will affect the bottom line. Maybe we should all lobby for better buses so there would be seats for 9 out of 10 guests.
I'm sure C&DE could tell us more, since he drove for WDW for so long, but it is my understanding that the "rows of seats" configuration is being universally phased out for mass-transit buses, because that configuration is a real problem for users of wheelchairs and/or walkers, who are a large part of the mass-transit user population. It is not just at WDW, but throughout the US and Europe. Newer buses don't seem to be built with rows of seats. It does seem to me that it is more economical in terms of fuel, personnel, and fleet size to plan for passengers to stand on most routes (express buses are an exception sometimes), and it also should mean that the bus will load and unload more efficiently.
Personally, I've always kind of wondered why WDW did not go to articulated buses so that they could move more people using fewer drivers (especially on routes such as All-Stars, etc.); but I suppose there must be some difficulty with maneuvering them. You would think that it would be cheaper to change the landscaping a bit, but I'm sure there must be other obstacles that I haven't thought of.
As to city vs. country viewpoints, yes, there are, especially when it comes to the "kids on laps" thing. There are also class distinctions that go along with those POV's. Most people who use public transit as an alternative to walking (as opposed to an alternative to driving) tend to see nothing wrong with unrestrained children on buses, just as they see nothing wrong with standing, as standing still beats walking near traffic and crossing city streets, especially in bad weather.
IME, the SOP procedure with kids on a crowded city bus is that you fold your umbrella stroller, get on the bus and put your kids in the seat. If possible, you find a double seat and put your kids in it; 3 will fit if they are small. Then you give the folded stroller to the oldest child to hold between his knees, and you stand next to them holding the bar or strap, with one hand free if at all possible. If you can't get enough seats together, you let the oldest either stand next to you or sit next to a stranger who is within your line of sight. Generally, the idea is to put the kids between an adult and a wall or bulkhead whenever possible, so that you can use your body to stop them from sliding out of the seat, and to keep them in sight, so that you can be sure that they behave themselves and get off when you do. Lap-sitting is also used sometimes, especially with the smallest kids, but most city dwellers prefer to put the kids in the seat while the adult stands, as you have more control that way and can better watch for your stop because you are facing the window. Usually the seatbelt worry is only an issue for people who own cars and consistently use seatbelts and carseats, as they are so used to hearing about how unsafe it is to drive without them. People who normally only walk or use buses/trains to get around tend to not pay a whole lot of attention to seatbelt/carseat warnings, since the vehicles they ride in don't accomodate them.