Yes, there are entries in there, but without the for clause it creates a histogram with a bucket size of 1... The optimiser doesn't consider this as a histogram.

If you create a histogram, you will see more entries for the column.

e.g. (on my db)

analyze table t_entity compute statistics;
select * from dba_histograms where table_name = 'T_ENTITY' and column_name = 'COUNTRY_ID'
--> 2 rows selected

analyze table t_entity compute statistics for columns COUNTRY_ID size 75;
(75 is default)
select * from dba_histograms where table_name = 'T_ENTITY' and column_name = 'COUNTRY_ID'
--> 14 rows selected

Terry