The HP is a 515MB download, while the Epson is a 972MB download. Both updates were released today and are available via either Software Update or from .
The update installs the latest software for your Epson or HP printer or scanner. And that is pretty much all anyone needs to know, as Apple takes care of the gory details.
If you're curious, feel free to check out the list of all or printers covered by this update.