I think it is representative of MN. Because a lot of us posting throughout the day are sahms/housewives who have the time to do so.
A good number of us doing so, are enabled by DHs income, as in his income is high enough to not require me having a second income for the household.
The household income of two professionals on £60k mean neither exceed the £80k threshold, but combined household does. Many people are in this situation, but they're at work, not posting on online forums during the day.
DH is on 6 figure salary. So, there's really no need for me to add a marginal amount to that with a part time job which will essentially get wiped out with the childcare costs. And that's why I'm at home with the ability to post on MN as and when. For balance though, technically it's not my income, so whilst DH falls into that bracket, I, on the other hand very much don't.