No an organization can have one process. Infact many companies utilize one software development methodology (sdm) for the entire organization. Often times one can not. A case in point. I work for a company that is under the umbrella of a regulated agency. Most, but not all systems need to be validated. If the software doesn't fall under the regulated umbrella, we don't validate - we use a much lighter SDM. If the software does fall under the umbrella, we user a very heavy (formal) SDM. We try to reuse as much as possible, but sometimes is just is not worth the effort.