They won't issue a subpoena for a fishing expedition, there has to be at least some evidence.
However, I don't think that this is a real issue, as competitors and the most skilled customers already mostly know how the devices work. Also, both Xilinx (AMD) and Altera (Intel for now, but looks like the might spin it out) have so many patents that it's probably mutually assured destruction and a huge gamble if either sues the other. I think they just prefer having the tools proprietary, not just to lock the customers in (though they like that) but also to keep away from the hairy corners (avoid defects in the hardware design that could produce bad results or fry the chips).
However, I don't think that this is a real issue, as competitors and the most skilled customers already mostly know how the devices work. Also, both Xilinx (AMD) and Altera (Intel for now, but looks like the might spin it out) have so many patents that it's probably mutually assured destruction and a huge gamble if either sues the other. I think they just prefer having the tools proprietary, not just to lock the customers in (though they like that) but also to keep away from the hairy corners (avoid defects in the hardware design that could produce bad results or fry the chips).