Thatcher funeral: political or protocol?

From today’s New York Times:

The official American delegation named by the White House was led by two more [Kissinger was there, but not as part of the official delegation] former secretaries of state, George P. Shultz and James A. Baker III. But some British Conservatives complained that President Obama did not send a senior serving member of his administration.

Bloomberg adds:

Asked if Cameron thinks the U.S. had snubbed the U.K., the prime minister’s spokesman, Jean-Christophe Gray, said“absolutely not.” “The seniority of the dignitaries in the U.S. delegation that includes two former secretaries of state with whom Lady Thatcher worked with very closely herself, is testament to her global stature,” he said.

I think this is odd. And I’ve no idea if this is a breach of protocol or is protocol. All the news stories make note of this, but the criticism I’ve seen so far seems to be coming entirely from the right.