I'm afraid that you misunderstood me. What I said is that people often use "which" before a restrictive clause, where you would have us use "that", not vice-versa.
So, for example, according to the rule book, we should write:
a)Presidential elections, which occur every four years, are the main events.
b)Presidential elections that do not result in a majority are often contentious.
People do NOT say:
c*)Presidential elections, that occur every four years, are the main events.
and I didn't suggest (or mean to suggest) that this is correct usage.
But people do often say and write sentences such as the following"
d)Presidential elections which do not result in a majority are often contentious.
I would have no compunction about writing such a sentence, even in a formal paper. Nor would most writers. The so-called "rule" which (sic) prescribes using "that" in restrictive clauses (like (d) ) was invented more than derived from observation of actual usage.
By the way, here's a short quote from Fowler's "Dictionary of American Usage"
"The disctiction between restrictinve 'that' and descriptive 'which' or 'who' is an invention of the grammarians and a very recent one. Fowler, who recommends it, says, 'it would be idle to pretend that it is the practice either of most or of the best writers.' What is not the practice of most, or of the best, is not part of our common language."
P.S. To close on an agreement:
Yes, I agree, commas are missing from the sentence you cited. And yes, I agree, substituting "that" for "which" does indeed change the meaning or your last example.