Apparently psychology seems to show that people get excited to see a low starting price (even if they don't know the reserve) and once they start bidding gain an emotional attachment in thinking they could get a deal. When their bid is under the reserve, they may be more inclined to increase it at that point a few dollars at a time hoping to meet the unknown reserve price.

As your example let's say a buyer decides $100 starting bid is too much and doesn't bid. If it starts at $10 with a $100 reserve, this person bids $70 as the high bidder hoping it is enough. Now they are thinking; didn't meet reserve, so I'll up my bid by $10 thinking $80 is still a pretty good deal. At this point they have already made a couple bids and start dreaming how nice that would look on their project bike. Eventually they say,Why not bid another $10? Now they start thinking in terms of the small additional increment of $10, instead of the $90 because they fritter away $10 at Starbucks every couple days etc.

I agree that an auction with a disclosed reserve doesn't seem to make much sense.