> I see no technical need to do a clustering of superpeers

It's common sense

> I thougt superpeers are designed to help also normal clients
> e.g. to shield the weakest members (modem users).

That is only one benefit of Ultrapeers, but you can do much more with Ultrapeer technology. Not only can you shield modem users from heavy traffic, but by clustering Ultrapeers together, you can increase the search horizon of all Ultrapeers and the clients connected to them.

This will make the end users happier, as they will more likely be able to find the file they want in their larger horizon. Isn't that important to you Moak? That the users of gnutella clients are satisfied with the results the receive?

*Note: Adam Fisk already posted a picture illustrating how Ultrapeer clustering achieves a higher horizon.