IPTV, whether live or streamed, is not carried by a protected protocol (such as TCP) where dropped packets would be re-transmitted by the far end. If a packet containing IPTV gets dropped - for whatever reason; bit-errors, congestion etc - it causes a glitch in the video/audio.
It doesn't matter what amount of buffering occurs - that glitch can never be recovered.
G.INP activates limited retransmission across the weakest part of the whole end-to-end segment (whether multicast or unicast): your copper connection. It isn't quite a guarantee that the packet gets through (which TCP would do), but it improves the odds no end.
