Performance Tuning :: Adaptive Cursor Sharing?

I have a table "t", with a highly skewed ID column
Cursor_sharing=force
select count(*) from t;
--79003
select count(*) from t where id=1;
--79002
select count(*) from t where id=99;
--1

I have a index on id column and since highly skewed data is there in id column therefore histogram is there

SQL> select table_name,column_name,histogram,num_buckets from user_tab_cols where table_name='T';

TABLE_NAME COLUMN_NAME HISTOGRAM NUM_BUCKETS
------------------------------ ------------------------------ --------------- ------------
T ID FREQUENCY 2

When i use literals , explain plan comes up with optimal execution plan
select * from t where id=1;
Full table scan

Select * from t where id=99;
Index range scan

But when i use bind variables,sub optimal execution plan

For id=1, it should use Full table scan but it goes for Index range scan , WHY? why ACS is not getting kicked?

alter system flush shared_pool;
set autotrace traceonly
variable n number;
exec :n=1;
select * from t where id=:n;

[code]...

Why is_bind_sensitive not "Y"?