I've just deployed maas and juju in my saucy installation. And I found there are no charms for saucy. I think I need to include cs:precise for all charms. Why? Saucy is now released.
Most charm authors only release charms under the LTS release unless the charm is not functional on the non-LTS releases. If you are having an issue deploying a charm under saucy your best bet is to contact the charm author for an update. Since charms are designed for software deployments in production environments we recommend using an LTS.
Saucy only has a support life of nine months, while LTS releases will be supported for over 5 years. As such, server deployments (and by association, charms) are targeted at LTS releases of Ubuntu (precise, trusty). Charm authors can choose to provide versions of charms for other Ubuntu releases, but it's not a requirement.