Of course not all of them stay. Some go home, armed with valuable trade secrets with which they bring a product or service to market at an even lower cost and an even better chance of success, having escaped R&D costs.
I just love being a consumer.
And, don't forget the anxillary benefits for the home country: applications that will improve defense (or offense) posture on the world stage.
Is this a great country or what? By the way:
You know, I'm wondering what happened to all that concern about domestic security that was so much in evidence just a few weeks ago, on capital hill.