An online reviewer, Jim, remarks:
Well, "summarize" and "summarizeItem" were fairly simple one-liners. Not much to break there. But "matchingSum" was longer and possibly worth testing, at least to my non-Smalltalk trained eyes. Perhaps an experienced Smalltalker would disagree and say that "matchingSum" was obviously correct.
I think Jim is probably right. When we wrote the method, it just flowed out in good Smalltalk style. But as I mentioned above, Chet and I looked hard at it, hoping to make it more clear. We couldn't think of anything, and it was working fine, so we stopped.
On another day, I might experiment with breaking out the lookup aspect of the object. It kind of seems like overkill, but there's a common behavior one ...