I think the problem with this thread... and with 2filter's claims... is a misunderstanding of price fixing. Price fixing is contrary to general laws of supply and demand. Where there is true price fixing, the market supply does not adjust itself according to consumer demand. Price fixing, as I said above, would prevent the laws of supply and demand from operating. It is illegal because consumers are hurt in the end.
From what I understand here, and why outbri above can make a case, this does not seem to be a case of price fixing. Price fixing occurs amongst competitors. It would be price fixing if Hoya, BW, and Tiffen got together and decided to not sell filters below a certain price. This is illegal because it is collusion and creates a effective monopoly. It is not price fixing when a manufacturer contracts with several retailers and requires that the retailers sell their products at certain prices.
In short, it's not price fixing when only one manufacturer is involved. It seems sneaky to require a retailer to sell at a certain price rather than let the retailer decide his own profit margin based on how much he paid for the filter from the manufacturer... but there's nothing wrong with it. I think it's called vertical price fixing, which is fine.