Part of it is software licensing that charges per-socket or per-core. For Sun they do have certain applications in mind that are very parallel, such as web ser

Part of it is software licensing that charges per-socket or per-core. For Sun they do have certain applications in mind that are very parallel, such as web serving and message routing, where memory latency can serve to slow things down; the idea of hardware threads is to keep the CPU busy in spite of waiting for a fetch from main RAM.