Obviously it was a mistake.
It's also obvious that Obama doesn't think very highly of the "special relationship" between the US and the UK.
Compare and contrast the thought and care that went into Brown's selection of gifts for the Obama's and the our president's clear indifference in the reciprocal effort.
In the arena of High Diplomacy, such indifference is tantamount to insult.
There are people who are employed by the White House to make sure protocol is honored.
This gift debacle suggests one of a few things
1) Obama's staff is utterly incompetent
2) Obama doesn't care enough about our relations with the UK to even show interest in protocol
3) Obama was deliberately sending a message to the UK
I would expect nothing less from Obama supporters than blithe dismissal of the matter as perhaps a humorous mistake, but certainly "no big deal."
While I am actually surprised by said supporters loss of the ability to perceive the ironic, the irony is clear and obvious for anyone with clear vision to see.
Whatever the reason for the snub, we should know what it is. It's an insult to our national intelligence to assert that it is meaningless --- nations have gone to war for such diplomatic "mistakes," and if the Administration is going to make such a big deal out of "restoring" diplomacy to our foreign policy arsenal, we should at least expect it to understand all of its intricacies.
But hey, if you insist on giving this Administration a pass on incompetence or are willing to mistake design for simple error, so be it. Not really a surprise.