Whether UDP or TCP is used, to have a reliable transfer, packets have to be acknowledged. (In the case of UDP, the application itself must generate the acks since the protocol doesn't.) Thus the same reasoning applies as to the other question you referred to.
Saturating the "up" part of your Internet connection slows downloading because packets coming "down" have to be acknowledged by your computer and those acknowledgements have to go out via the up link. If your computer falls too far behind in acks because the up link is choked with data, the sender will slow down and start retransmitting the unacknowledged packets. This will appear to you as a decrease in download speed.