I've read at least twice that throughout its latest history (the last ten years) AMD managed to create only two new CPU architectures, K8 and Bulldozer.
All AMD CPUs between K8 and Bulldozer are more or less the same design, and that fact alone explains that even Phenom2 CPUs offer modest improvement in IPC and power consumption over original Athlon64 CPUs which were released over 8 (!) years ago. All these CPUs share the same functional blocks, the same cache hierarchy, the same number of core blocks, etc.
Meanwhile during this time Intel has gone through Merom, Conroe, Wolfdale, Kentsfield, Arrandale, Clarkdale, Lynnfield ... the list goes on and on. Every 2-3 years Intel offers some radical improvements which made Intel the king of the hill since the advent of the Core 2 architecture.
Also we have to bear in mind that Intel's R&D's budget equals AMD's entire revenue, and since the x86 architecture is one of the most complicated computing architectures (at least from what I've heard), maybe the fact that AMD is always trailing Intel CPUs is that AMD just lacks resources to innovate and invent (actually resources are there but senior managers in AMD have indiscreet bonuses and salaries which means they don't have as many talented engineers as e.g. Intel can easily afford).