IIRC the main point about not doing so is "We're going to ensure that this body of work has so many legal threads hanging off of it that it ensures no single agent can track them all down and relicence the work otherwise.

While, IMO, the FSF & other non-profit agencies are an appropriate holding body, I would seriously have issues with a for-profit company asking for a CLA for open source work. I would instead reply with a request for a Statement of Work & some cash...