Questions about partitioning and ext3

[JEMF]

Hello all!

I have a 512 MB Kingston flash disk. When I try to create a partition 
with 460 MB (471.040 KB), the partition is created with 460.6 MB 
(471.665 KB).

------------------------------------------------
   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1         951      471665   83  Linux
------------------------------------------------

Why? Geometry?

2nd Question:

When I format the partition with ext3, the df -k command returns:

------------------------------------------------
Filesystem           1K-blocks      Used  Available Use%  Mounted on
/dev/sdb1               456730       8239    424908   2%    /mnt
------------------------------------------------

I think 8239 KB (8.05 MB) was used by journal. But the amount of  blocks 
decreased after formatted (471665 to 456730). Why?

Thanks.