...what about older users? Should we just dismiss their needs?
If their "needs" are to have every app look and behave exactly like some obsolete physical object, then frankly yes. Old people are not incapable of learning or adapting, and they've already had to do just that for many years now.
Are interfaces really encumbered because they feature a wood-textured background?
Bit of a strawman, there. When Apple revamped the Address Book app for Lion, they made it into a "book". Gee, sure looks nice! But suddenly you couldn't use the old three-pane view (which showed more information and was just better at navigating many contacts) because it didn't fit into the "book" metaphor. Not only that, but being a "book" implies lots of things that you couldn't actually do with Address Book. As John Siracusa wrote in his Lion review:
Address Book goes so far in the direction of imitating a physical analog that it starts to impair the identification of standard controls. The window widgets, for example, are so integrated into the design that they're easy to overlook. And as in iCal, the amazing detail of the appearance implies functionality that doesn't exist. Pages can't be turned by dragging, and even if they could, the number of pages on either side of the spine never changes. The window can't be closed like a book, either. That red bookmark can't be pulled up or down or removed. (Clicking it actually turns the page backwards to reveal the list of groups. Did you guess that?) The three-pane view (groups > people > detail) is gone, presumably because a book can't show three pages at once. Within each paper "page" sits, essentially, an excerpt from the user interface of the previous version of Address Book. It's a mixed metaphor that sends mixed signals.
The three-pane view is kinda back in Mountain Lion, but you still can't adjust the relative sizes of the panes (presumably because the two sides of a real book are always the same size). This restriction makes no sense for a digital contact app and makes the app less useful, but it's dictated by the designer's slavish devotion to the book metaphor. A minor thing perhaps, but as a designer, you should know that these little things can quickly add up to make a product utterly (and needlessly) frustrating to use.