The question is really that simple: is Debian stable a rolling release? If it's not a rolling release type OS, does a rolling release distro exist which is based on Debian stable?
I know Debian unstable and Debian testing rolling release distros exist already.
You're right, Debian stable does not have a rolling release model in so far as once a stable release is made, only bug fixes and security fixes are made. As you said, there are distributions built upon the testing and unstable branches (see also here). What is it you're expecting from a rolling release distribution based on stable that is not satisfied by one based on testing?
I guess what you're looking for is Debian CUT, a proposal to create a "Constantly Usable Testing" release. I haven't followed this closely, so I have no idea if this proposal is endorsed or within reach.
As far as I know, Debian doesn't have a rolling release model. At some point no new packages are added to the repositories and only bugfixes are provided. In this case you can upgrade your system to newer release.
Good examples of rolling release model is Gentoo, Arch, ... where in fact there are no formal releases - you simply upgrade gradually.
If your /etc/apt/sources.list reference squeeze, you are on the 'stable' release and as such, it is not rolling. It is feature locked every year to two years.
However, it is my understanding that if your /etc/apt/sources.list points to testing or sid you are on a rolling release because of the way packages enter the system.
