While in general I agree with you, as I said in another thread if the GM is running a facility that would have much, much, much more planning and brainpower behind its defenses, the only way to make it realistic is to include some stuff that wasn't there before the players announced their plans. I haven't been forced to do it yet, but I freely admit that I am not the strategic or tactical equal of what the corps would have to throw.
In this specific case, however, you're entirely correct.
Edit: and rereading, everything I stated above could fall under a "good IC reason", which means you're right in every case. Never mind
~J