Quoted from ovfdfireman:
No reason really, Dealers taking a small deposit on the Special and Classic to know they are serious buyers. The only reason why someone may want to preorder is because they will be first in line to get them. To some people that matters, getting one fast. People that commit to a game will have one placed in their name right way, and it will never go to stock.
I get why people don't want to pay up front (that's a choice), I also understand why dealers do not want to "call it sold" without a small monetary commitment. I expect only a few classics and a few specials out of the gate, so if I tell people I am sold out and send them to buy elsewhere, I want to be sure they are in fact sold.
It is very common to put 5-10% if you want to reserve or hold an item,that seems fair. However, that is clearly the buyers option whether they would like to hold one or not.
I am cool either way!
Actually there's one pretty significant difference I'm surprised you left out - in this case, the manufacturer requires the deposits from the dealers, who in turn require it from their customers. That's highly unusual, and it's a pretty clear play by the manufacturer to get an influx of cash prior to building.