Keeping copies of a company's accounts for tax purposes, and keeping copies of everything they make and sell, isn't the same as keeping copies of private signing and encryption keys. They might be held in escrow, and they might even be available to Congress on request under very controlled circumstances, but I doubt very much that Congress keeps a copy. Even if they did, how is that relevant? The fact that the Government has a right to see certain data doesn't mean that it is automatically in the public domain and freely available for anyone to use.
The fact that Microsoft doesn't need the backups because they no longer run the service DOESN'T mean that they'll just sell the backups. Like all sensible companies they would DESTROY the backups once they were legally allowed to do so. If your uncle was even slightly knowledgeable about computers he would know this. My uncle also saw computers evolve, but knows nothing about data retention and disposal policies - just like your uncle, it would seem. There's a world of difference between using a computer and understanding the detail of the technical and legal environment that computer companies operate in.
Why do you persist in believing that Microsoft should release their proprietary data? The fact that you believe they should do so is of no interest to Microsoft. They own the code, and the data, and the private keys, and even if it is currently of no direct value to them they are unlikely to release it, for a number of reasons:
1. It may be of value to them in the future.
2. It almost certainly contains code or methods for which Microsoft owns the patent, and which they therefore wish to protect.
3. If any part of any patented code or methods has been licenced to others then Microsoft is still making money from that licence and will wish to retain that licence income. It is equally likely that the terms of any such licence prevent Microsoft from making the code publicly available, in order to protect their licencees from any potential competition or attack.
4. It almost certainly contains code or methods licenced from other vendors, which Microsoft has no right to release because it belongs to other people.
5. There is a strong possibility that it contains code that has been carried forward into the Xbox 360 Live service (because programmers will re-use code wherever possible), and therefore releasing it publicly will expose any back doors that exist in the code, thus providing an attack surface for the current Xbox 360 Live service.
I'm sure lots of "people would be more happy if" they had their own dedicated Xbox Live servers. They'd also be more happy if they lived in a mansion and owned a string of fast cars and never had to work again, but that doesn't mean someone will give them that lifestyle.