To clarify (?):
* No device will protect you, if you got the wrong address to start with.
the discussion was about finding methods to prevent that,
BIP70 with a correctly enforced certificate chain being one suggestion, in which the device can help (by enforcing said certificate chain)
Exactly. AFAIK Trezor plans to implement this BIP once it's accepted (It's in the final draft stage now). But provided that BIP70 is used, device may be able to protect you against address replacing malware.
Assuming however that everybody you want to send bitcoins to can be certified in that way. What if the address-switching malware does its trick only on non-secured addresses?
By the way, I do not see in the BIP-70 write-up an analysis explaining why it would be secure against malicious browsers and apps. I see only a
claim that it is "more resistant" to them, but no explanation why. Is that obvious?