According to the equation given in this article, strength is part of the power equation. Speed, I would guess, is what Joe Friel calls "speed skills". He says that the term isn't the same thing as velocity, i.e. how fast you're riding. It means being able to perform the required movements of cycling quickly and efficiently: rapid pedaling without bouncing all around in the saddle, and I believe it also refers to handling skills, such as cornering.
Many a time I've wished I had a place away from traffic where I could work at cornering. Unfortunately, parking lots are apt to be full of hazards such as broken glass and other litter, even when there aren't many cars going in and out. On top of that, I usually don't have time for both practicing such skills, and simply getting my ride done. I choose the ride, and hope the interval work I'm doing builds enough strength for me to have better power.