I've seen this claim several times, but I don't understand why exactly such a route would be necessary. Could you elaborate a bit?
Some networks are not routed via the IPIP full mesh but directly via the Internet. For example Sweden and Australia announce their network directly via BGP but at the same time it seems that they don't have IPIP full mesh access.
As such if you want to reach any of those networks from within the IPIP full mesh, you will need to route your packets via a default route for 44/8 to the UCSD router which can then route the packets towards the internet.
The reason why you cannot just inject your packets to the Internet via your own Internet upstream lies in BCP 38 (http://tools.ietf.org/html/bcp38), which btw is a good thing for the internet as a whole (I admit in our specific case it's less useful, but still...).
73 de Marc, LX1DUC