HTTP Age Header Field (Section 14.6) - should overflow value be 2^31 or (2^31)-1?

Section 14.6 of RFC 2616 states that if a cache receives an age that is
larger than it can represent, or if overflow occurs, then it must transmit
an Age header with a value of 2147483648 (2^31).  Was the intent to select
the largest unsigned 31-bit integer, which is really (2^31)-1, or is there
some other rationale behind this choice?

MD