A few thoughts I might add:
I likely picked up the NAPA stubby pear head below in the mid-late 80's new from a NAPA dealer (making it one of the very few ratchets I've ever bought new off the shelf, my 5 Craftsman RHFTs being a good part of the rest). This thing is smoooooth as buttah, the smoothest MDF pear head I've ever held (and I've got a few...).
My experience so far has been that the pear head Craftsmans generally don't work as smoothly as some of the pear heads branded for others - have a set of NOS K-Ds that are pretty smooth (but not quite as nice as that NAPA) as well as some other NAPAs. I've always wondered if perhaps the Sears contract specs may have been less rigorous or more tolerant of minor variances (like internal finishing/polishing/spring quality/etc) than some of the other contracts Moore and later EASCO serviced. Could also be that the other brands/contracts came along later in the patent life of the pear heads and benefited from some minor enhancements/refinements that Sears didn't want to spend additional on.
As rough as some of the pear head Craftsmans I have are, I've yet to find any EASCO Arnold patent ratchet I like (the modern "figure 8" cover plate), and I've got a handful of brands there as well, including NAPA, Kobalt, Menards, and even a couple of S-Ks. On second thought I'll take that back - the Kobalt and NAPA 1/4"s are pretty good and have seen some routine use.
Maybe I'm mis-reading, but I get the feeling that there's some thought that Sears had a pretty heavy hand in determining their specific ratchet designs and when they moved permanently from one design (like the pear heads) to another (the Arnold patent). While I think they did in overall broad ways - like the universal inclusion/requirement of quick-release part-way through the pear head years to current and handle shape - my expectation is that the major shifts from one patent design to another were more a result of what EASCO was moving forward with and retiring old designs than Sears getting very specific in engineering all-new designs. The Arnold patent was applied for in 1991 and filed in 1993, which generally concurs with their appearance and the demise of the pear head. The patent drawings however are knurled round handle with one flat handle/raised panel drawing as prior art. The quick-release mechanism is pictured as well.
My guess is cost/unit played a really big role too, especially in the finer details and minor changes over time, with Sears maybe accepting a lesser degree of finishing, wider variability in quality control specs, even lower cost materials in some instances (plastic reverse levers instead of metal, etc) all to keep the costs down with EASCO deciding where/how they could save a little and still meet the contract. Going cheaper in areas like those would also offset the expected increased cost of including the quick-release mechanism too, or at least I'd think so.
The RHFTs were likely already on the EASCO drawing board or in late development when Sears went for them as an all-new Sears Best design - I have those RHFTs in several more bands than pear heads, and the quick-release is not exclusive to Sears - it's the most common variety, with non-QR only found in a couple brands alongside QR models. Other than different grip styles and some exterior finishing I've never noticed any difference in the quality of operation in any brand.
I'd really like to hear what Lauver and some of the other Craftsman gurus could add/clarify.
