Both AMD and NVIDIA provide access to this extension across all of their 3.x and 4.x hardware. It's high-time this was core behavior.
And no, glMemoryBarrier doesn't cut it. Besides the fact that it's not available in 3.x land, it doesn't do what glTextureBarrierNV does. Texture barrier is all about framebuffer object writes; glMemoryBarrier only is concerned with writes via atomic counters, image load/store, or shader storage buffers.