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Some "radials" especially cheap ones and in off-highway applications are actually ~89 degree angle bias ply construction. Different construction method than true radials, but approximating a radial enough to be called one (I'm looking at you, Carlisle).
I have heard that the feathered/diagonal heel/toe wear can be due to worn out shocks/struts, but that also causes a "cupping" wear that is further apart than each tread block. Poor steering geometry can cause the heel/toe wear if your driving puts you in situations where you are frequently operating in turns where your steering has a very off-Ackermann geometry, but this would be driving style-related and nothing mechanical that could be fixed on your vehicle.
Note that suspension modifications can cause changes in steering geometry even if the alignment can be correctly adjusted. A suspension drop will change the angle of the tie rods on a rack-and-pinion setup to a different degree than it changes the angle of suspension arms. This can increase bump steer and change the Ackermann variance curve. Some of you folks that lowered vehicles to reduce drag but drive in city conditions a lot may experience some weird tread block wear because of Ackermann error induced by suspension changes. Typically OTR Class 8 trucks are designed with 100% Ackermann at the steering angles required for Interstate highway curves, but take that same tractor onto city streets and Ackermann error increases tremendously at increased steering angles. I would hazard the safe bet that most automobiles sold in North America have similar design features.
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