Stephen, your missing 1/2 the point of the A/C system. Vapor compression systems are designed to remove heat and humidity.
You could have an A/C system that takes 79F air from the room, runs it over a coil at 77F and it would return at 78F but there are two problems. First, with that low of a temperature difference, the coil would have to be huge to get enough heat transfer to occur. (Heat transfer is directly proportional to surface area.) Second, there would be no moisture removal. Since indoor environments contain things that generate moisture (people, coffee makers, showers, etc.), the moisture would continue to rise until it hit something around 99%.
The cold temperatures arise from the need to remove moisture. A surface colder than the dewpoint, such as a glass of ice water outside on a humid day, will cause moisture from the air to condense. This is what your A/C unit is doing. It is dropping the coil temperature to around 55F or less to remove moisture from the air before returning. It blows it out at those cold temperatures so you don't waste money on a much larger fan to premix the air before it comes out.