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