the problem is that it's an unprovable assertion. nobody can tell whether you've kept the private keys. all a thief would have to do in your place is keep all the data, inspect the block chain periodically for a very large balance, and strike once many years from now in an entirely untraceable way.
Of course. YOu are 100% right. But what is different here is my ass is on the line. Thief should plan on his ass being kicked if he is giving out his real name and address like I am. MtGox and MyBitcoin could stiff you any second, and your bitcoins could disappear if they get hacked (as has already happened to some). I also have enough personal assets that one could sue me for losses and actually recover them. If you suffer a substantial loss at the hands of MtGox or MB, you're lucky to get the time of day.
i actually trust you, and i doubt i could name five other members of this forum i would say that about. but sadly i would not be able to recommend a service like this.
Just curious, would you also say the same for MyBitcoin.com?
it wouldn't be much harder to set up a website that uses the right sort of handshake to prevent you from ever knowing the private keys, and then outputs a pdf that the customer can print. why would anyone prefer the physical post here, unless they don't know how to print a document? (the post adds an additional problem, which is that the document might be inspected by a post officer or any other 'man in the middle'.)
The closest practical thing I can think of would be something in Javascript that generates the private keys client-side, so the server side never sees them. That would be trivial to do. But that doesn't really solve the problem - one must then trust that the website is being honest about the behavior of the script and that one's own machine isn't compromised by malware. The typical person interested in a paper bitcoin wallet lacks the expertise to independently determine what such a website really does.