Does network distance to a server affect throughput ?
Downloading from more distant servers will be generally slower than testing from servers near you.
This is an excellent illustration of why broadband internet connections should be tweaked for better throughput from distant servers (see the TCP Optimizer). Windows is not completely optimized by default to utilize broadband connections over high-latency networks, such as the Internet.
HTTP is technically bound by the TCP "congestion window" which determines how many packets can be sent at one time. The larger the window size, the higher the throughput. Latency directly affects this because slower responses will create delays between packet sends. As a result, your throughput will be lower to more distant servers. This can be compensated by tweaking Windows settings to better utilize your broadband connection.