[r6rs-discuss] Why are fx+ and fx* restricted to two arguments

[Mikael Tillenius]

In section 9.1 fx+ and fx* are defined as taking exactly two arguments 
with the following comment:

"Rationale: These procedures are restricted to two arguments
because their generalizations to three or more arguments would
require precision proportional to the number of arguments."

I still don't understand why. The programmer must make sure that no 
overflow happens (or be prepared to handle the overflow) independent of 
the number of arguments. Two arguments may overflow as well as ten.

I can see many reasons for having more than two arguments. E.g (define 
(intensity r g b) (fxdiv (fx+ r g b) 3)) when I know all of the 
arguments are between 0 and 255.

Can someone enlighten me?

/Mikael