"All X are not made equal" - ambiguous meaning?

Solution 1:

I think OP's first example is probably a misuse of the phrase being discussed. I can only imagine it being said by someone who has doubts about whether to actually own a car at all. A more commonly-applicable version with minimal changes is...

Well your Ford is good, but not all Fords are [made] equal.

The word "made" isn't necessarily part of this "stock phrase". In this particular case it can be included, because cars are manufactured. But that wouldn't be the case in, for example,

Well, your rottweiler may be safe around babies, but not all dogs are equal.

I see no justification at all for OP's assertion that "every X is different to every other X" is a logical corollary to "not all X are equal". This is simply incorrect. The meaning of the expression is at least some X are not the same as the others (or ...not the same as the one just mentioned).

Effectively, "not all X are equal" is a stock phrase used to point out that just because one particular X has some characteristic, it doesn't automatically follow that all X's have it. Usually with the strong implication that a significant number of X's don't have that characteristic. So my first example might be said by someone who's just been advised to buy a Ford, by a friend who cites his own good Ford as justification for the advice. The speaker is simply pointing out that this justification is based on faulty reasoning of a type Wikipedia calls hasty generalisation .