That's the policy but I wouldn't count on it.
nginx is an awesome piece of software, but it's still almost a one man project, without a public bug tracker, without the kind of infrastructure of other projects with a similar user base.
Igor has declared 1.0.0 stable and probably won't backport bug or security patches to the 0.7 or 0.8 branch, so you'd be counting on the nginx community and/or debian or ubuntu maintainers.
The old server wisdom is that you stick with old, stable versions and backport any bug/security patches from new versions. But some projects, including nginx, don't really lend themselves to that model.
You don't have to stay on the bleeding edge of the development svn, but I'd recommend sticking with what the project maintains as the stable branch.
That's my opinion, anyways.
