It is trivially simple - IF YOU do it correctly
You access photos for upload using the media browser - on the left of the upload window under media ==> photos ==> iPhoto - as well documented in this forum and in these forums
see the use tip on accessing your files for a complete discussion of this
You seem to confuse "easily" with "the way I expect".
For help accessing your photos in iPhoto see this user tip:
It'll show you how to easily find and share your photos.
You need to have a photo or album highlighted / selected / open, then hit file - export.
I was very frustrated by this for a bit. I was also able to get into the library by selecting file - reveal in finder - original file, then was able to drag and drop the masters folder to a backup disk.
Bad idea - going into the iPhoto library directly is NOT supported and is very dangerous - you should only use the supported access methods - either export or the media browser - How to Access Files in iPhoto
and as to exporting - obviously you can not export a photo until you first select it - clearly you need to select the photo(s) and then you export them - not possible to do it in reverse