The issue is also reproducible with JBoss 7 and JBoss EAP6 on Windows Server 2003 R2 and is related to general TCP flow control issues of Windows Server.
The TCP flow control is slightly improved with Windows Server 2008 / 2008 R2 but still not as optimal as on Linux.
German article on TCP flow control on Windows(fee-based):
My recommendation for internationally used systems is, to host either on Linux directly, or to put a Linux-based reverse proxy (e.g. Apache) in front.
I found out that the main reason is the default network configuration of Windows.
The download performance improves massively after tweaking the network configuration with registry settings, see IBM Websphere article(German):
I've increased also the TCP default receive and send window sizes, see article:
After the tweaking Windows network performance is raised to the niveau of Linux