Cheating is cheating. It barely matters with whom one decides to cheat.
An in-home worker is simply easier...with whom to fall into some sort of inapproprate relationship since they've already been invited into the intimacy of the family home.
And in celebrity homes where a nanny, for instance, is required because at least one parent (or spouse) is often absent, its only more likely to happen. People - even famous ones I imagine - like a sense of family. Even if that may mean that busty Nanny No-No has to fill in for mommy in more ways than one.
Also, its a perfect cover for a chronic cheater. It takes just that much more time to fully figure out that its an affair - with kids in tow - rather than just a lonely daddy with the nanny & kids because mommy is too busy running a Fortune 500 company.
Its why the gardener or cabana boy is so popular with the rich married ladies in return. It takes at least half a summer season for people not just to joke that mommy is flirting with him but that, instead, there's a whole lot of extra-marital whoopie happening out at the poolhouse.