You could also add D-Link or Linksys NAS products to your short list - but at the end of the day, none of them provide the functionality that Windows Home Server will - it is much more than just network attached storage.
Sure most of the consumer NAS products also lets you stream media and ship with some sort of backup software, but how well do they work - can you do a bare metal restore?
One last thing - which of the available consumer NAS products allows for secure remote access, not only to the files stored on the NAS product, but to the desktops on the network - to the best of my knowledge - none.