I believe this is an insecure method to send Bitcoin as there might be several wallets in the same IP.
Moreover, the Ip address reveals their location.
I was also surprised to see this thread and the discussion is just amazing. We had so many way outs back then and IP address was considered one of them. I don't know may be back then the IP address or as such internet was not everyone's cup of tea and thus it was limited by its interaction. If Satoshi is alive today then he might have already laughed at his own idea of sending the Bitcoin's to IP address. The world has changed a lot and internet has become complex network with more chances of cyber attacks if your IP is breached.
Bitcoin would have not survived. It would have been hacked now and then by smartest high school kid too! That much weak this system would have been. I think it's worth that developers had debate on this back in the time and they changed this protocol. Nice walk through the history of mechanisms.