As someone unfamiliar with the differences between those OSes, could you elaborate on why you would expect them to compare CoreOS in particular and why I or someone else might also want to consider it for similar purposes?
CoreOS is essentially built for running containers, which is how Google have described the Debian 7 image deployed in this preview. CoreOS has a number of features that are really geared towards running it as a bare metal OS (won't elaborate on that here, their docs do a good job of explaining), which is not the use case here so can't really blame Google for going with something more familiar (to them).
CoreOS is a linux distro specifically created to support containerization. It has great Docker support and a built-in distributed key/value store and a container manager for orchestration and service discovery.
> It has great Docker support and a built-in distributed key/value store and a container manager for orchestration and service discovery.
Is there more to this? Most OSes have great docker support (Ubuntu et al) and etcd (the kv/orchestration tool you speak of) is open source and available to most distros as well.
CoreOS' most noteable feature is the fact that it is incredibly light weight and fosters a modular enviornment that (IMO) is less likely to be plagued by dependency hell related issues that you might tolerate from other distros' package management system (Not talking about you Portage, your still coooo).
CoreOS does this by utilizing Linux containers via Docker to easy–bake applications through individual containers of which are explictly isolated from eachother, aiding in the problem of static/dynamic shared libraries causing dependency issues.
Now you can of course utilize all of this on a distro like Debian, and even borrow the best of CoreOS like etcd (for one example).
TL;DR; CoreOS features awesome concepts and services like etcd, and fleet, and more that doesn't mean you cannot do the same with Debian, but it won't be native, and it would not be very light weight out-of-the-box compared to CoreOS.