Moving from the tactical idea generation phase of design to implementation can leave some details left unchecked. Why? It's hard shifting from debating broad and loose concepts with a team to individually plugging away on task driven items. The implementation phase of any design project can be an isolating experience. It doesn't get the same peer review as the strategic and tactical phases of a project.
After staring at the Yahoo player, I realized that some of these implementation details were overlooked. At first glance the video tool bar seems fine- it's modern and relatively simple. As you begin to analyze the spacing, every element is slightly off. Icon alignment, spacing between buttons, left and right margins, and horizontal alignment are all tweaked.
Is it laziness on the designers part? Maybe. More than likely it's an oversight in the transition of broad ideas to refined implementation ready graphics.