I think the speech and preparations could have been handled differently. It is tragic that veterans, friends of veterans and families of veterans could not visit the memorial on Memorial Day. I belong to none of those groups but had I been visiting DC over that weekend I too would have been angered at not being able to see the Wall.
That being said: clearing an outside venue for a presidential appearance is incredibly difficult and time consuming; people would have been angered on any day they could not have visited the Wall or any other memorial along the Mall in DC because of a president's appearance.
Had they opted to do a speech by the President indoors, then run it on news shows with a backdrop of the Wall and/or other memorials, I think some in the right wing media would have used that as backing for their news flash "President Afraid To Be Seen In Public" or "President Disses Vets By Not Honoring Memorials In Person"; a perfect catch-22 situation, especially in an election year.