>> The less housing there is in a braking system, the less housing compression there is; the less compression there is, the more positive the braking is <<
Duh!! Why didn't I remember this ?? I think that Larry has hit the nail on the head.
In general, braze-ons were used for many centerpull bikes, because centerpulls already have more slack in the system because of the straddle carriers and lesser mechanical advantage. Braze-ons were also present on bikes with brake-lever extensions. In fact, it seems that the correlation is highest between centerpulls / extensions and top tube braze-ons, which supports larry's conclusion.
- Don Gillies
San Diego, CA