In large part, that's because many of the things that actually improve the home are not visible. So someone out looking at new homes doesn't see a lot of what makes the home better, and so if not informed, doesn't take it into account. Take insulation for example. One of the best innovations in recent years is sprayed in foam, the best known of which is probably Icynene (http://www.icynene.com). The great thing about these products is that they seal up every crevice and crack, nook and cranny, inherent in traditional residential stick-built construction. So there is nearly zero leakage and infiltration of undesired hot or cold unfiltered air. In builder parlance, the house is "tighter".
In the photo, that stuff up in the roof rafters is Icynene we put in a recently constructed home. (The walls are John Manville's Spider fiberglass insulation, also sprayed in, but not a foam product, which we can discuss another time. http://jm-builder.com) If you were to ask many builders -- probably most -- they'd say that using this product will cost about three times what conventional batt insulation would cost. But I heard an argument from Carl Seville, a well known Atlanta green building consultant, that using Icynene in the roof actually can save construction dollars. We at First Street Builders have been doing it under the assumption that it was costing us money, but doing it nonetheless because it is truly a better method. But here's Carl's argument that takes us back to the title of this post. We can do attic insulation to code, or we can do it "right" (use and protect the batt insulation correctly, caulk all leakage to and from the attic space, insulate all the ducts adequately and carefully, etc), or we can do it "really right" with foam. As it turns out, "really right" foam is actually less expensive than "right" with batts. It's quicker, and better in virtually every respect than the old ways -- even when done conscientiously and as effectively as possible.
And this "better but hidden" idea applies to so many things in a house. Did you know you can get a guarantee for the lifetime of the house against floor squeaks from iLevel by Weyerhaeuser (www.iLevel.com)? But the buyer can't see the iLevel floor joists (except maybe in the basement, and even then probably doesn't know what he's looking at). High efficiency HVAC systems look pretty much like low efficiency systems. Ditto for water efficient fixtures. Ditto for power saving light fixtures. The list goes on and on.
If you are a builder, a home buyer, a home owner, or a real estate broker, I invite you to dive into this new world of GREEN building and be an informed participant in the single family construction game. The green playing field is changing every day, so there's a lot to keep up with. For those of us in the business, it's an opportunity to differentiate ourselves from the pack, and a way for us to truly serve our home buyer clientele.