I haven't played ArchitectureCraft myself, but looking at the user manual provided online, I see a few things:
1. Overlays - Carpenter's Blocks allows overlays of grass, snow, vines, web, hay, or mycelium on (afaik) any of its blocks. ArchitectureCraft has a brief mention of "cladding" in the user manual, but it probably doesn't include all of those possibilities, and only allows them for roof blocks (so probably not railings).
2. Illumination - Carpenter's Blocks allows its blocks to glow while still being disguised as other blocks.
3. Decorative redstone components - Carpenter's Blocks has special versions of levers, buttons, daylight sensors, and pressure plates that can be set to resemble other blocks. Also, the pressure plate can be configured to control what entities trigger it (defaults to players only iirc, which is handy for a crop farm to make it simpler to get in and out without letting animals in)
4. Decorative doors, gates, and garage doors.