It was previously my job (for 3 years) to investigate security breaches and destroy devices. You are almost uncannily correct.
>I doubt the components are backdoored by default in stock hardware. More likely, GHCQ was worried that other nations (China, Russia, etc.) were targeting Guardian journalists in an effort to gain access to the Snowden cache. As such, GHCQ probably was simply taking extra precautions in the event that hostile intelligence agencies had installed implants into the Guardian's hardware.
This is it in a nutshell, and, legislation states they had to physically destroy the devices. It was not optional. It was the law. There is absolutely nothing more to it.
> [Edit to Add]
Believe me, I have destroyed the brand new iDevices of senior Government personnel because they plugged it into a classified network to charge it for less than a minute. The law is the law. I actually had a wall of digital devices we had drilled, degaussed etc etc. The Guardian were treated the same way we treated everybody. I had my phone confiscated cause I stupidly did the same thing at the start of my career. shrug
There really is no story here which makes the cloak and dagger theories even more funny. It is almost cargo cult-ish. Some guys at Cheltenham will be rolling in the aisles reading these comments.
> [Legislation Guidance for those asking]
You can Google and read the statutes and policies yourself.
>> Once the classified material had been confirmed, security operators were then legislatively bound to destroy or other render unusable the material in question.
The legislation which required all reasonable and necessary measures are contained within the Official Secrets Act 1989, the National Security Strategy, the Data Protection Act and the Regulation of Investigatory Powers Act 2000 with detailed policy guidance promulgated to intelligence operators via HMG Information Assurance Notes (1/2 (SPF)) and, more importantly, HMG Information Assurance Note 5 and the Joint Services Publication 440 which governs counter-compromise measures.
Ultimate responsibility for HMG security policy lies with the Prime Minister and the Cabinet Office. Departments and Agencies, via their Permanent Secretaries and Chief Executives, must manage their security risks within the parameters set out in the framework, as endorsed by the Official Committee on Security (SO).
All HMG employees (including contractors) have a collective responsibility to ensure that government assets (information, personnel and physical) are protected in a proportionate manner from terrorist attack, and other illegal or malicious activity.
The loss or compromise of such Critically Important Assets would have a severe, widespread impact on a national scale and Departments must work with the National Technical Authorities and the Cabinet Office to ensure they are afforded appropriate levels of protection.
[EDIT TO FURTHER ADD]
I have posted the links to 7 policy and legal frameworks. If you cannot find these documents or you are still asking then frankly, you are too fucking stupid to trying to analyse the law or most other things.
People on HN are not your legal secretary. You not being able to find something is not proof of it's absence.