Neither "idiolect" nor "counterfactual" are neologisms. They are common words round my way. Anyway, please read the MWDEU entry I linked to.

My idiolect doesn't make any difference in meaning between

If I was the Prime Minister, I would change the law.
If I were the Prime Minister, I would change the law.

I know that both sentences are counterfactual, since the form of "be" is in the past tense, and the main clause has "would". I'm not sure how this variation is evidence of deterioration.

In fact "be" is the only verb that has a special form for the counterfactual. With ever other verb, we use the simple past, for instance:

If I lived in Paris, I would visit the Eiffel Tower.

Writers have been using "was" and "were" interchangeable for about 300 years: http://books.google.com/books?id=2yJusP0vrdgC&pg=PA877&vq=subjunctive&dq=merriam+websters+dictionary+of+english+usage&source=gbs_search_s&sig=Oy0dCbCw5SCr5alz6IIx61tNYoY#v=onepage&q=subjunctive&f=false

Brus, you cannot assistance something because "assistance" is not a verb, it's a noun. A gerund is not a noun, because you can't replace it with a real noun, like "assistance".

As AnWulf has said and everyone seems to have ignored, "that" and "who" used interchangeably isn't the fault of Americans, or young people, or lack of education. Using the word "that" refer to people is part of normal English.
http://books.google.com/books?id=2yJusP0vrdgC&lpg=PP1&dq=merriam-websters%20dictionary%20of%20english%20usage&pg=PA895#v=onepage&q&f=false

"You must look at the root of the word."

That's the etymological fallacy. Etymologies aren't definitions.

AnWulf, replacing one word with a completely different word doesn't prove anything.

However, "oblige" does mean "To constrain, influence; to force, compel (a person)" (OED sense V.12).

Merriam-Webster's Dictionary of English Usage has an entry for obliged vs obligated. "When the constraint is applied by physical force or by circumstances… obliged and not obligated is used."

http://books.google.com/books?id=2yJusP0vrdgC&lpg=PP1&dq=merriam-websters%20dictionary%20of%20english%20usage&pg=PA675#v=onepage&q&f=false

Americans? Shakespeare couldn't get who/whom straight.

Albany. Run, run, O, run!
Edgar. To who, my lord?
- King Lear

Elbow. My wife, sir, whom I detest before heaven and your honour -
Escalus. How? thy wife?
Elbow. Ay, sir; whom I thank heaven is an honest woman.
- Measure for Measure

http://books.google.com/books?id=2yJusP0vrdgC&lpg=PP1&dq=merriam-webster's%20dictionary%20of%20english%20usage&pg=PA957#v=onepage&q&f=false

MDWEU on "real" as an adverb: http://books.google.com/books?id=2yJusP0vrdgC&lpg=PP1&dq=merriam-websters%20dictionary%20of%20english%20usage&pg=PA799#v=onepage&q&f=false

From Merriam-Webster's Dictionary of English Usage:

This construction, both with and without the possessive, has been used in writing for about 300 years. Both forms have been used by standard authors. Both forms have been called incorrect, but neither is. Those observers who have examined real examples have reached the following general conclusions: 1. A personal pronoun before the gerund tends to be a possessive pronoun (of course, with "her" you cannot tell the case). Fries 1940 found that the possessive predominated even in letters written by the less educated. 2. The accusative pronoun is used when it is meant to be emphasized. 3. In speech the possessive pronoun may not predominate, but available evidence is inconclusive. 4. Both possessive and common-case (uninflected) nouns, including proper nouns, are used before the gerund.

There's lots more: http://books.google.com/books?id=2yJusP0vrdgC&lpg=PP1&dq=merriam-websters%20dictionary%20of%20english%20usage&pg=PA754#v=onepage&q=gerund&f=false

There is a set of words that is usually only used in questions and negatives. For instance "any" and its derivatives.
I didn't see anyone.
Do you want any eggs?
*I saw anyone.
*I want any eggs.