I think it goes the other way; the manufacturers' obsession with thinness (for mostly aesthetic reasons) goes a long way to explain why they're focusing on reducing power draw.
It's great that they are reducing power draw, but by making everything thinner (usually translating into decreased power storage), those gains in efficiency are largely cancelled out when it comes to battery life in real-world usage.
When creating these things, the designers, engineers, and marketing people obviously have some kind of target battery life in mind, and it seems as though the target is always "about the same battery life as the last generation," whereas there's no end to the number of compromises and engineering efforts that go toward cutting 1 mm off one dimension.
And of course, the tech bloggers all go nuts about how thin the newest generation is compared to the last, and people buy computers based on their recommendations.
Aren't these things thin enough already, at least for professionals? Why not go for some truly earth-shattering battery life on one of these laptops? Do people really care more about that 1 mm than they do about potentially hours of additional battery life?