"image_meta" contains a mix of both EXIF and IPTC meta data, but only a fragment of it. I do not see any of my keywords in WP's "image_meta". It would appear that WP doesn't utilize them (a quick check with an FTP client reveals that the data is preserved in the uploaded file, but it doesn't "move along" to any other image sizes that WP generates).
FWIW, a brief explanation might be useful for you:
"EXIF" contains the more technical data about the image, like aperture, camera, copyright, etc. - this part of the meta data is usually embedded in the image data by the camera, when it is stored on the camera's memory card.
"IPTC" contains descriptive information like the location, title, caption and keywords. This part of the meta data is commonly added in an image editor or digital asset management system.
"XMP" is a different/newer approach that contains both EXIF and IPTC data, as well as post processing information about the software used, etc. (most common among files created by software from Adobe).