TransactionStateData and AbsoluteTime

Hi, I'm wondering why the transaction star time in
TransactionStateData is Absolutetime. From nabstime.h:

* Although time_t generally is a long int on 64 bit systems, these two
* types must be 4 bytes, because that's what the system assumes. They
* should be yanked (long) before 2038 and be replaced by timestamp and
* interval.
*/
typedef int32 AbsoluteTime;
typedef int32 RelativeTime;

Shouldn't we use timestamp instead of AbsoluteTime in
TransactionStateData? It also gives more precision.
--
Tatsuo Ishii