I had a E-2 visa back in the 80's and early 90's before I became a U.S. citizen and everytime I came into the country, U.S. Immigration never asked me what kind of plane ticket I had. In fact, they never asked to see my ticket. The permission to stay in the U.S. was always for one year even though the visa was valid for five years and the presumption was that one would leave the country, at least temporarily, every year. I used to go up to Canada and come back to the U.S. after a weekend and thus "reset" the one year clock. There were times when I travelled by car to YVR and flew back on a one way ticket and I never had any problems.

Sorry I don't have any recent experience, especially post 9-11 but if you were worried, you should call the airline and the U.S. Embassy for clarification. The E-2 visa, although non-immigrant, is treated differently from a tourist visa IME and U.S. Immigration is not as concerned about over-staying. Hope that answer some of your concerns.

And welcome to FT!