Martha Stewart did a somewhat curious thing last week: She talked tablets with her followers on Twitter. No, not pills, or some arcane French revival furniture piece. Tablets, as in computers. “Serious question,” the crafty decorating and cooking maven asked readers on Dec. 12: “How many of you will read magazines on an electronic tablet (interactive-full color) within two years? three years?” This is notable, because when Martha Stewart talks publishing, people listen.