Alignment issue, or trait of the Prius?

There's your problem. Toyota's recommended pressure of 35 psi front, 33 psi rear, is too low. Wear on the shoulders of the tyre with tread remaining in the middle is consistent with underinflation.

Try 38 front, 36 rear, or a bit more front and rear if you're willing to put up with a slightly harsher ride. Higher pressures may also improve handling, up to a point.

 

MattFL,

I suspect that you're thinking along the right lines; most likely an
alignment issue.

Seems like the cars sometime see some rough seas or careless
handling on the trip over. The pre-delivery prep by the dealer is
supposed to include an alignment check and a 12 V battery full
charge. All too frequently it seems from the reports here, one or
both of these procedures aren't done -- an informed buyer would be
wise to insist on getting a copy of the dealers internal pre-delivery
check-off sheet and reviewing it carefully before the sale... no
tickee, no washee.

Hopefully you're within the 1 yr period since purchase so you take
advantage of the one free new car alignment. (I forget the mileage
ceiling, sorry.)

Hope this helps.

 

You can check your front wheel alignment. However, excessive tire shoulder wear is a Prius characteristic, and is one reason why many owners use 42 psi front, 40 psi rear (another reason is to slightly improve realized mpg.) Higher tire pressures will help to make tire treadwear more even across the tread.