maybe trezor v2. will have the 'webwallet' on the device next time. that way it can auto run on offline computers without the need of web extensions or communicating to trezor server.
then your free to push the TX to any miner/network user you choose.
i think those believing trezor is infallible have never thought of a hacker tweaking the web extension to do man in the middle attacks..
The trezor basically only generates the tx (by signing it a-la how any bitcoin client works) and the webwallet pushes it. The trezor is basically the 'offline computer' factor in a secure wallet setup. The only 'sensitive' (where anyone with that public key would be able to see your future transactions, but not spend any of your bitcoins) date would be the public key which is transmitted to the 'webwallet' in order to show you the transactions made by the addresses. MiTM attacks are handled by the fact that the actual addresses are shown on the screen before the device signs it, so when the address is different from the one you're planning to send to, you'll know there's something fishy up there. The TX itself is not a valuable information as at worst the attacker can only refuse to broadcast it. Having the tx itself is not beneficial in any way as the hash would be invalid if any changes were made - as in where a PGP signed message cannot be modified without invalidating the signature itself.
Electrum, Multibit and a few others are amongst examples of independent softwares utilizing the fact that you're basically free to push the TX to any miner/network user that you choose. You can run it on any offline computer by utilizing the command line/API that comes with it obviously.
Full disclosure: I recently bought a trezor after using Armory on an offline netbook for a few years (when I escrowed a lot). I've studied the source code and understood how it actually works before plunking down the cash for it, and I'm currently writing some tools for it.
Thanks for explaining in depth! I didn't want to quote franky1 posts above (I don't agree with his explanations) as you have already explained everything and with the knowledge that I would never be able to explain with.
In lamest terms, when I was buying a Trezor and did a research and decided to put my savings on it, I understood that this device is the safest way out there to store my bitcoins and that even if Trezor company ceases to exist I will be able to recover my coins and also that it's not that easy to insert a malicious code in it. To some extent you still have to trust them as you trust Electrum developers out there with every new release for example!