I agree with you that there is a spectrum of risk taking from gambling to investing. Nevertheless both involve taking risk and expecting payoff sometime in the future. Both the estimate of risk and estimate of payoff could be wrong or could change dynamically. I wouldn't be surprised if some argue that US government bonds are more risky than investing a diversified portfolio of forex today.

I guess you could equate them by saying investing in government bonds is like betting on a team paying $1.01 to win. The odds are vastly in your favour to gain from the investment but it's not certain.