Re the 1st one: it's true only if the transporter doesn't risk anything if the sensor is tampered with. As soon as you introduce strong fines and/or consequences if a validating authority randomly checks your goods and discover some tampering, the system is a bit more likely to be trusted. But of course, in such a case, you might as well just host the temperature log with the validating authority (like it's done for Concrete, or in the Auto industry).
The second one is even more compelling: of course the trust chain stops when the trust chains stops ! But if every luxury Louis Vuitton handbag is tracked and you know precisely whether it's been sold or whether it's supposed to be sitting on a shop shelf somewhere, you have zero risk of double sell (or at least, within the same limits as a bitcoin double-spend).