It's because there is a betapatch out which all the servers are allready running.
An official patch should be out next week orso, but if you want to play online and see the new patch now download this
http://forum.1cpublishing.eu/showthread.php?t=25901
and unzip it in
"C:\Program Files (x86)\Steam\steamapps\common\il-2 sturmovik cliffs of dover"
(or on whatever drive you installed Steam and CLOD)
The new sounds should be a nice surprise for you
