Trouble with capitalisation and wget 1.9.1 ?

[Loul]

I'm a TOTAL newby with gnu.
Basically I'm a windows XP typical user and I wanted to download some 
specific files from a specific website without typing all the urls.

So I got hold of the latest wget for windows there 
http://xoomer.virgilio.it/hherold/ which is the 1.9.1 complete

(I had the 1.7 version but it wouldn't seem to behave properly as there was 
a ? character in the starting url).

And well I went mad not getting why my command line wouldn't work.
I eventually used wGetGUI to go through that nightmare.

But I wanted to get why it didn't work and here's what I found out :

wget -r -l1 -A.AVI -H -Dwearepes.com  
"http://www.wearepes.com/iboard/index.php?showtopic=7767&st=0";

would work

but 

wget  -r -l1 -A.avi -H -Dwearepes.com 
"http://www.wearepes.com/iboard/index.php?showtopic=7767&st=0";

wouldn't work !!! (actually this script was used for downloading videos of 
tricks for a soccer game on the playstation 2... not something really 
important :) ).

The only difference is that I typed the extension using lower case letters !
And didn't found any explanation in the documentation I read.

So bug or feature ? 
Thanks for your help :)