The Ebay website is far from unique in the design cruft that has accumulated on it. You could argue that the problem isn’t so much with the web designers, or even the product people trying to shift their particular block onto the real estate, but the twin problem of a  desktop-sized display with a  pixel-accurate mouse interface. The Ebay app looks beautifully streamlined on the iPhone and the iPad, and the common factor here is the display size and the touch interface. Basically, the twin pressures of a small display coupled with a chunky touch interface (chunky in sensitivity compared to a mouse) force mobile designers to design in large, discrete blocks, which also happen to help streamline data rendering.
The proof of this for me is that mobile sites and apps often feel kind of chunky and under-designed when mapped onto a desktop monitor. I suspect it’s not just the display, but the fact that the mouse interface encourages pixel-sized interaction, whereas the touch interfaces are completely in the other direction. In other words, where do you ‘click’ on a mobile site? This could be ameliorated by changing the nature of mouse from ‘clicking’ to ‘touching’ – i.e., deliberately ‘degrading’ the sensitivity of the mouse, from a desktop perspective. I suspect the main culprit here is the mouse interface itself, and not the screen size, resolution, location, etc.
Perhaps Ebay-style websites could be redesigned along more effective principles if the nature of mouse/screen interaction was rethought?