Unneccessary cmax in heap tuple ?

Hello,
Why is there cmax in tuple ? cxxx is used to determine
if tuple was inserted/deleted by current command or
past command. Because one command can't both insert
and delete the same tuple, only something like "cupd"
might be needed and flag which tells you whether cupd
is time of insert or delete. This saves 4byte from 
header .. 

devik