Thanks - I went to the Apple store & asked them the same thing -- could they download it to a thumb drive for me. They said no but I am welcome to bring the iMac there & use their wireless. You can't even buy it on disk.
The reason they can't do it for you in that respect (off their own machines) is that it requires an iTunes/App Store account to do it so - in my experience with Mavericks and Yosemite, if you were to copy the install.app from someone else's machine to yours when you attempt to install from that it will ask you to log in but it'll crap out on you when it comes up and tells you the installer was tied to someone else's account. Again, that's been my experience and I've seen that happen a few times where friends are like "here's a copy of my <whatever version> installer.app, just copy it from the USB stick (meaning the stick isn't the installer, it's just got a full copy of the installer.app) and then run it..." only to find out it's tied to the other owner's account.
While creating a USB stick from the installer is relatively easy, I haven't been able to create a bootable ISO so far. The instructions I used for Yosemite which created such a thing don't appear to work the same for EC and I'm not sure why at the moment, will have to continue to do some research to find out what exactly has changed. The Yosemite instructions will create the ISO but it won't boot, odd but I suppose I'll figure it out at some point.
So far so good with the final version, however, no complaints here but I had none with the GM candidate either in the time I used that.