I'd like to offer an explanation as well since I was thinking about this for my physics final tomorrow morning. I think definitions of these terms helps: wavelength is the distance 1 cycle travels and frequency is amount of cycles in a given time. Equations aside, you have two waves, one of longer wavelength W1 and one of shorter wavelength W2. I see it as if they both travel a certain distance, you'll see that there are fewer cycles of W1 than W2 because its wavelength is longer. Because there are fewer cycles for the wave with the longer wavelength, its frequency is smaller. If the frequency is smaller, it's not oscillating as much and therefore has a smaller energy. I hope that was logical!