Magazines HAVE to sell copies.
Putting someone like Cheryl on the cover, guarantees them good sales for that month.
Why do you think Kate Moss does 2 Vogue covers a year? They have to keep the circulation at a level to please advertisers, who ultimately pay for the magazine.
I imagine that Victoria Beckham did extremely well for Vogue last year, so them doing Cheryl is a win win situation.
Who cares that she isnt a model or a 'vogue girl', she is one of the most famous women in Britain at the moment and i know for a fact that EVERY other glossy in Britain put in a request for her.