"Where/how does a "five minute rule" change this (regardless of the item being sold)???"

You are assuming that no one else has bid after your $100 hypothetical bid. In your scenario ... suppose there are two (or more) bidders submitting artificially high bids? Let's take your artificial $100 bid on a $1 opening minimum, which ebay now shows as only $1.00 bid, and someone like Skip "I won't be outbid by anybody" unknowingly bids $90. How much do you now pay for your ebay gamesmanship?

The "five minute rules" allows those procrastinators, or those who do not have software progams, to monitor a particular ebay auction and bid along with the other bidders. Nobody wants to pay top dollar for an item that they can get for retail at most any chip show. How many times has a bidder said "gee, if I knew that chip or strike only went for $35 I would have bid more"? And after that bidder bid more under a "five mintue rule", the previous top bidder has another opportunity to top the new bid. The seller gets more for his item, the bidder has an opportunity of not getting shut out after the item gets to a point where there is no more bidding interest. It's more like a live auction.

Just one man's opinon.