You're either logged in or you're not logged in, right? For people who are logged in, there are tiers, ways of distinguishing between users, such as mods, regular members, anti-citizens and banned people. If you're not logged in, you're a visitor. Simple as. You can't distinguish between...
Steam on Linnucks, anyone? It'd surprise me, certainly.
Although trying to guess what would shock you is difficult, because if you're guessing it, it's unlikely to shock you.
Perhaps it's significant enhancements to the engine, bringing in the latest graphics technologies seen in other games, like some radiosity, better shadows, etc. But I'd be disappointed more than shocked if they rewrote the engine.