Personally, I don't have a problem with the child benefit being restricted to those below a certain salary. These sorts of benefits should be there to help those less well off.
However, from a technical point of view, it is a complete load of bollox that the Government are making out that there are problems dealing with how to get around the issue of 1 partner on £45,000 not getting child benefit, yet a couple on on £40,000 each would still get it.
It can very simply be dealt with, as they already have the mechanism in place and it's very odd they're making out there's this cliff edge.
For the purposes of the completely different Child Tax credit, HMRC write out each year and ask for confirmation of the household income from both partners. In the current tax year if the combined income exceeds £40,000, then there's nothing paid. If it's below £40,000 then there's £545 plus amounts if an approved child carer is used, whilst if the combined income is below £20,000, then they get higher amounts, plus further payments for extra children.
So they could use exactly the same data to restrict the payment of Child Benefit.
Bearing in mind HMRC also have PAYE and Self Assessment income details for everyone working, and for those registered, they know who's not working, so they've got the information readily available in 2 different systems already.
A cynic might say they've announced it to try and make out they're doing something, but then they can say sorry, we'd like to stop it for the well off, but it's not possible. Crap.