SQL & PL/SQL

http://download.oracle.com/docs/cd/E14072_01/server.112/e10592/functions112.htm
<i>n determines the nth row for which the measure value is to be returned. n can be a constant,
bind variable, column, or an expression involving them</i>

Why below SQL returns same result ?:|

select * from v$version;

BANNER
-------------------------------------------------------
Oracle Database 11g Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0      Production
TNS for 32-bit Windows: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production

with t(empno,sal,rn) as(
select 101, 720,1 from dual union
select 102, 850,2 from dual union
select 103,1250,3 from dual union
select 105,1700,4 from dual)
select
nth_Value(empno,rn) over(order by empno Rows between Unbounded Preceding
                                                 and Unbounded Following) as emp,
nth_Value(sal  ,rn) over(order by sal   Rows between Unbounded Preceding
                                                 and Unbounded Following) as sal
  from t;

EMP  SAL
---  ---
101  720
101  720
101  720
101  720