The racks were used for small panniers. Berthoud makes a model with just one strap, perfect for a light B&B tour, in conjunction with a handlebar bag for what you need during the ride. They also serve to carry extra clothes, folded up and attached with a bungee cord. (Aluminum fenders are sturdy enough to hold that much weight. For a full "camping" bike, you have more secure attachments of the racks.
Rack trunks and other rack top bags fell from favor in France in the 1930s. They affect the way the bike rides because they tend to swing from side to side... The technical trials established that on a superlight bike, the best way to carry a load is on a front low-rider. Turns out that is the best place altogether... with a front rack second best. Berthoud now is making a "classic" racktop bag, which is not based on a type of bag used on these bikes. I won't comment further...
I think the rear racks were a bit of a fashion thing, too. During the 1930s, there were only rear racks (see the photo of Jo Routens in the latest issue of VBQ on p. 4). When front racks became popular (as a result of the technical trials), many people were on the fence, concerned they'd affect the steering. So they spec'd both front and rear racks on the same bike in the 1940s. By the 1950s, front racks had proven themselves, and many bikes dispensed with the rear racks, unless the customers planned to do some light touring. (Even then, I'd recommend add-on low-riders instead of a rear rack, but that is a different story.) Today, we are undergoing the same evolution again, with the new Heron Randonneur having both front and rear racks for those not sure about the handlebar bag...
Finally, I don't think VBQ has an exclusive on the technical trials or anything else. You'll have to ask the organizer, Chris Kostman of AdventureCorps. But as far as I know, the goal is to have the event reported as widely as possible in the cycling press. After all, the goal is to give builders and "real world" bicycles some exposure, in addition to determining who makes the best machines.
The lack of color in VBQ is being addressed. I can't tell you more
for now... but the bikes deserve to be shown in full color.
Jan Heine, Seattle
Vintage Bicycle Quarterly
c/o Il Vecchio Bicycles
140 Lakeside Ave, Ste. C
Seattle WA 98122