ls versus du

Hi all,
I don't know whether this is a bug or not, but I will describe for you what I have noticed
I am using RedHat 7.2 with kernel 2.4 (using ext3 filesystem)
There are different outputs for these utilities while I expect the same behavior
$ls -al

and 

$du . -a -b --max-depth=1

The difference is in the sizes they show, there is no match between them, for example I have a file that its size is 201 bytes using ls and 4096 using du .
 
If this is not a bug?!! can you explain this behavior for me.
 
Regards,