I know the techtrees are old news, but I was just taking another look at them and I noticed something that doesn't make much sense to me.

The prereq structure for the Colossus, the Robotics facility, requires a Stargate in order to be built. Since Colossi are basically Protoss equivalents of siege tanks (heavy anti-ground support role) I'd expect them to be down in T2, like siege tanks, but are apparently higher up.

Anyone else find this a bit strange?

The Stargate is not a prerequisite for the Robotics Facility, only the Cybernetics Core is. It looks a bit confusing on the tech tree that you saw. Also for the Protoss tech tree it looks like the Stargate is required for a number of the different next tier buildings but in reality it is only required for the Fleet Beacon, the Robotics Facility is required for the Robotics Bay, the Twilight Council for the Templar Archives and the Dark Shrine.