Edit: For example, here's what the Guardian's style guide says on the matter:
http://www.guardian.co.uk/styleguide/c#id-3022716
Of course, with something as flexible and constantly evolving (and as used and abused) as the English language, it is usually possible to find examples and counter-examples for just about anything. There are also edge cases; the Guardian refers to police forces as plural entities, I believe. Suffice to say, when I was running a back bench, singular was the order of the day when it came to company names.
But then I never won any awards for grammar.
But for me, when speaking and writing consider companies to be groups of people, and so I use plural. And I think that is common over here in Britain.
That should be explanation enough.
I'm intrigued that you are ready to rule out the contributions of a class of people who manipulate the written word for a living (and debate usage among themselves to the point of distraction!)
ASDA? Well, I'd use "Asda" since it is pronounced as a word, not four initials. But the company itself still seems to be struggling for consistency on that...
(I wonder if British law considers a corporation to be a person to the degree that US law does, or if this plural view of a corporation is pervasive in law as well as in grammar.)