That has mostly to do with the fact that the title Engineer isn't thrown around loosely—most of the engineering grads I know are employed under the title Technologist (or something similar on the impressiveness scale). Engineer is usually reserved for positions with attached professional liability, and yes, the iron ring is part of that deal.
The iron ring has nothing to do with the Professional Engineer title. The iron ring is run by alumni of various Canadian engineering schools, and is granted to all students graduating from an engineering class with a Bachelor of Applied Science or Engineering. It's a symbolic gesture to remind graduates of their responsibilities to society, etc.
The title of "Professional Engineer" (P.Eng.) is reserved by law to those who are granted that title by the self-governing engineering bodies of each province (e.g. Professional Engineers of Ontario). You can't legally represent yourself as an Engineer in Canada unless you are a registered P.Eng. The title does indeed attach professional liability, and is a method of ensuring responsibility and safety in engineering projects.
