For people who are, if you believe the google stats, 'educated and decently off' the MN demographic spend a heck of a lot of time worrying about chaviness.
If you don't live near chavs, have to deal with chavs or have them puking all over your front garden, then I would imagine they wouldn't even register to you.
Brings me to the conclusion that a lot of the so-called stats are actually bollocks. Perhaps the MN demographic typifies a section of the UK population who want to get away from fears of chaviness rather than having succeeded in their efforts to do so? And this is why they constantly need to ask what is chavvy or what is MC.
A confidently MC or UMC parent would name their child whatever they desired. Same with confidently WC or 'chavvy' parents. They wouldn't need guidance from a parenting website. If you need to locate signifiers in an attempt to up your social standing then you are more likely to belong to an insecure class, whatever that might be.
Mumsnet is likely, over all, a mix of every class, but prefers to be perceived as better off (unless there's a housing thread, when all of a sudden all of these apparently aristocratic mums suddenly boast of being brought up on a council estate).