Can't see any other reason for this tbh
If the bidding in the auction goes above £100, then you'll not be able to see the indentities of the people you are bidding against. Seller can still see the indentities of all bidders though.
See here..
and here for an auction example.
Their reason, to reduce to number of scam emails going out as 2nd chance offers, but it just means people can use aliases or their mates to bid on stuff to bid on stuff and no one will be any the wiser. Thus eBay are on a win win by gaining more commission fees!
Superb idea!