I am fairly certain spawning was later modified after Halo 3 launched because of these same complaints. I think they did it around the time the melee became a big issue too.

Team-Locked Spawns are always a pain, but I can see why they seem like a good idea.

They just don't usually work. I use Team Initial Spawns on my maps, but the Respawn points are all Neutral. I have some Spawn Zones encouraging Blue Team to spawn on Blue, but nothing hard-forcing them. -shrug-

Pete can probably explain it. lol