To put it best, the old style of Discovery Island was very cluttered. They are still keeping the animal carvings, just toning down on them and muting the colors a bit so it doesn't look so messy.
I know a lot of people like the old, colorful design, but from a marketing perspective, think of it if you will. Look at the before pics of Creature Comforts and Island Mercantile. The designs on the signs were so cluttered, you barely could make out what the sign said or in some cases, the signs were very poorly placed. In the updated versions, the signs are crisp, clear and stay true to what DAK is while still making sure you can read the sign (and if you know it's there, you're more likely to come in and shop).