When building my app, I started just using the Theme.Light.NoTitleBar.Fullscreen theme. I built all my layouts for the whole app like this, and got things to look how I want them. Some drawables used in the layouts have their size specifically set, and others are set to wrap_content.
I then decided to switch to the Holo light theme. When I do this, all the drawables used in layouts that are set to wrap_content end up larger. Almost as if they are pulling from a larger bucket. In fact, some look like they've been stretched.
I know the background is black in the older theme one, but that's not an issue (this is actually a layout file that is included in another layout). Obviously there's quite a difference in size between the two.