LONDON — For all the talk about one big, globalized art world, the trans-Atlantic gulf reasserted itself the other evening via a small but telling event. An overflow crowd of several hundred people, young and old, men and women, gay and straight, packed Starr Auditorium at the Tate Modern here to pay tribute to David Wojnarowicz, the artist and AIDS activist who died, at 37, from AIDS, in 1992.