[tsimionescu]

Well, 3.141 is an approximation of pi, not a representation of it, insomuch as you use it in an arithmetic expression. Of course, you can write 3.141... to just represent pi, but you can't eaisly use that in an arithmetic expression. For example, I can't tell you from "mechanical" operations if 3.141... - 3.1417 > 0, I have to lookup how big pi actually is.