For windows, specifically, you do want the characteristics of old growth lumber. The stability matters a great deal for a window. You don't want your windows to

For windows, specifically, you do want the characteristics of old growth lumber. The stability matters a great deal for a window. You don't want your windows to stick because the sashes are warped, and the increased rot-resistance of the heartwood helps ensure durability despite imperfections in the paint job. Everything you've said is true for general construction, but the fine article is addressing windows specifically.