I think it's pretty much significative to see that over the 4 times the championship title decided on a collision over the last 20 years, the FIA took a sanction in only 1 case, in 1997, while the one who caused the incident had already lost the championship. In the 3 other cases, the one who got it caused the incident but got no sanction. I guess it would have given a pretty bad image to F1 if the champion was disqualified from the season in 1989, 1990 or 1994, no matter what he's done to get his crown. Just imagine, you can't disqualify a driver straight away, you need to make him go through the FIA consil, and it takes time... I'm sure that a championship decided 1 month after the end of the season was the last thing the FIA needed.
Yea, okay, the championship was eventually decided on after race penalties in 1989, but this hadn't much to do with the incidents - unless you consider Balestre made Senna pay for it even if he wasn't on fault, which is probably what happened in the end