[pessimizer]

You're confining gambling only to casino games or games with vigs (http://en.wikipedia.org/wiki/Vigorish). Under your definition, when I play cards with my friends for money, I'm not gambling because my expected return is zero. Actually, judging by my known skills in any particular game vs. my partner's skills, what I'd be doing would be varying nightly.

What you're saying seems to be a useful distinction, though, but I'd say it's the difference between "risk entertainment" or something else and investment, rather than gambling and investment, because it's all gambling.