There is at least one auction house (it may be Goldberg) that allow you to specify an incremental bid or halfbid in the event of your highest bid being matched. Seems a good idea.
I still have a problem with the case you illustrate. If I submit a maximum bid of, say, £500, I expect the lot to go to at least the next bidding step to overbid me. I think that is a reasonable and logical assumption. So, when the auctioneer takes my bid of £480 in sequence and asks for a bid of £500, he should in my opinion have to take a higher bid to outbid my commission bid. But clearly, this doesn't necessarily happen.