The only reason for ST tires is so tire company's can sell a tire with a higher stated load capacity and lower speed rating. They are are not a superior tire to an LT, in reality with few exceptions they are an inferior tire. I will stick with LT's on my 5er as they are work great and don't have blowouts all the time.
The trucking industry doesn't use different casings for trailer tires. The tread pattern might be different on them depending which axle they are on, steer, driver, or trailer, but they all use the same casing. That casing might be capped as many a four times, and have close to 300K on them or more.