She was found within 3 weeks, involved a juicy story about her mother's involvement, and was on the tails of the Madeline McCann case so served to keep that one in the papers too.
The middle class argument wasn't that it was only covered initially, but that it is still covered 4 years later.
And the press were still reporting on Shannon Mathews mum coming out of jail just a few weeks ago so I fail to see the difference. I honestly don't believe in this class thing.