It's exactly how Vegas 1 worked, and that was never changed
There's a part of me that actually thinks its worse. All the time I spent playing Terrorist Hunt in the original, and I never actually saw one pop right in front of me. I've had it in Vegas 2 already at least half a dozen times, and I've only had the game about a week.
The sad thing is, if they had all the terrorists pop on startup, I'd imagine coding the range check to ensure that only those in the vicinity are alerted to your presence would be rather easy.