Alas eBay does seem to lend itself to sniping. Afraid I do it myself, but manually and generally I'd say you get a better price. You do of course still risk being out-bid, but far less chance of the price just creeping up to your maximum since any other bids on the auction will be "winning" until that point. I guess the psychology of people seeing interest in an auction and thinking, just another few quid? I think most people don't really want to commit what they are really willing to spend on something because it feels like spending the money despite the proxy bidding system. There must be a bit of legacy also in seeing auctions on TV where people interactively increase their bids, letting eBay do it on your behalf maybe just feels wrong to people?
I'd have lost on the above auction either way - Since the eight knights are probably worth at least £80 and well with the condition and clamshell £100 is probably still a decent deal these days. However I didn't particularly want the miniatures for any reason (okay they'd be cool to have) so I might have bid £30 at the last moment (hoping for a bargain) if I'd remembered and would have been out-bid by someone else's last minute bid.
I guess snipping is just sealed-bids really.