why so big?

I've just created a new database and I am wondering...

Why are all sequence files 8K?  They're one freaking int.

How come the indexes are so large?  They tend to be larger than the
database files themselves.  In one case I have a 16K index on an empty
table.

    -rw-------    1 postgres postgres       0 May 11 19:12 category
    -rw-------    1 postgres postgres   16384 May 11 19:13
category_parent_key
    -rw-------    1 postgres postgres   16384 May 11 19:12 category_pkey

    -rw-------    1 postgres postgres    8192 May 17 03:35 message
    -rw-------    1 postgres postgres    8192 May 12 13:26
message_id_seq
    -rw-------    1 postgres postgres   16384 May 17 03:35 message_o_key

    -rw-------    1 postgres postgres   16384 May 17 03:35 message_pkey
    -rw-------    1 postgres postgres   16384 May 17 03:35 message_p_key