According to a forum partcipant on Microsofts WHS Forum dated April 28th, 2011,
"Here is what I received from Avast! this:
Good morning,
Thank you for your reply and sorry for the confusion. As per the message which Jakub sent to you, we are certainly working on the Windows Home Server for WHS 2011 and hope to release it as soon as possible though I cannot give a specific date at this point.
I hope this helps, if not, please don't hesitate to contact me again.
Best regards,
Adam Riley
Third Party Support Manager
[Please reply leaving the message intact so we can see all the previous correspondence. Thank you.]"
Apparently because of so few WHS 2011 users, it is not high on Avast's priority list.