In the examples used in the quoted piece, you are talking about two distinct groups, but the key is that they both begin with the same qualifier, the same key to the subject -- everything on the table and everything in the cupboard. They are expanded into two groups, but they are part of the same root -- everything. It could just as easily be stated as "everything on the table and in the cupboard was smashed." The verb, "was", depends on the true subject, which is "everything", which is singular. In that case, "everything" has been expanded into two sub-groups, but they are still part of the same singular subject. It is the same with the other examples he used.

In the case of "wear and tear", that has come to be regarded as singular simply because they are always used together, they are partners in crime, they form a singular idea, as he noted. "Twitter and texting" are not at that point where they would generally be accepted by society as representing a singular idea, regardless of whether or not DK meant them as a singular idea.

That's my take, anywho.