That is a huge part of it. We have some friends who went through the process only 15 short years ago. She came to Canada as the dependent of her mother, who was applying in the SW class. Our friend got a work permit as a result of this SW ap for her mom, and she met her future husband on the job. After a couple years of dating, her work permit was expiring and Mom's SW ap had not been finalized. She was going to have to go back to Trinidad - so (as he now tells it) he said, "I guess we're getting married". After the wedding, he went with her to her exit interview and the CIC officer thought he was her lawyer. When he revealed that he was actually the husband, the CIC officer fell all over them and couldn't stamp her paperwork for permanent status fast enough. She walked out of that office with her PR - not even an application to submit. Shortly thereafter her mother's status was also finalized and the couple went on to have two children and a happy life. Unfortunately, Mom went back to Trinidad and lost her PR status - and now that she has health issues, she can't be sponsored to come back. She is almost completely alone in her country as her surviving children all stayed in Canada.
We are also friends with a man who came to Canada almost 40 years ago, from the States, as a Minister. After a year or so an officer from CIC knocked on his door and asked him whether he intended to stay in Canada. He said that, yes, he'd like that very much. So the officer told him just to go get a chest xray done and come down to the border and they'd stamp his papers. He did as he was told and was given permanent status on the spot - him and his family. They've been here ever since.