Zoom and focus ring placement

Does anyone know why Canon's intermediate lenses, like the EF-S 17-55 mm f/2.8 IS USM and the EF 28-135 mm f/3.5-5.6 IS USM have the zoom ring in front of the focusing ring?

Where is the logic in that then the more exclusive lenses in Canon's program, like the EF 24-105 mm f/4L IS USM and the EF 70-200 mm f/2.8L IS USM, share the opposite arrangement, with the focus ring in front of the zoom ring, with low-end lenses like the EF-S 18-55 mm f/3.5-5.6 II and the EF 28-90 mm f/4-5.6 III?

I could, perhaps, have understood if the professionals, who often use L-lenses, had different preferences than the beginners, and the intermediate then belonged to one of these two groups, but I can't understand the similarity in arrangement between the L-series and the cheapest Canon offer, with the lenses in between being the other way around.

Anyone?

Sometimes ago I've heard that ring placement on the L zooms is more suitable for heavier bodies with grips. Anyway, focusing ring on L lenses is more convenient for use - on zooms it is like on primes, while mid-range zooms have much narrower focusing ring. Cheapest lenses have focusing ring of simplest construction and probably simplest engineering solution is to put it at the front of the lens.

I think it has more to do with where the focusing group is in the lens rather than any pattern.

Actually I did think about that, so I checked on some lenses. But no. Lenses with ring type USM often have the effective focus drive at about the same place. Then it's just the designer's choice if the manual focus drive comes in from the rear or from the front. The differential gear between motor and manual ring lends itself equally well for both arrangements.

It has to be some kind of principle, but I'm not smart enough to see it through.