Hi Luke,
Sorry for not matching your expectations... There are a variety of those, too.
In general, yes. All of the image we generate can be copied to SD card and will boot.
Because many images require Linux filesystems and many users only have Windows PCs, we often distribute images as ".img.gz" packages that include a partition table and one or more partitions. These can be restored using zcat and dd under Linux or Alex Page's USB Image tool for Windows.
Other times (usually when there's only a single partition), we distribute normal '.tar.gz' packages, and you'll need to use fdisk or gparted to create a single partition (partition 1), and format as ext2/3/4.
The Ubuntu Raring image I pointed you at is in the .img.gz form and instructions for restoring the image are in the blog post.