to Tdol & Naamplao: another sentence about "be true of/ for"

[joham]

MacMillan English Dictionary, true:

1. The students are excited and the same holds/ is true for the teachers.

2. It rains a lot in the northwest, and that seems especially true of Cumbria.

Dear sir, would you tell me what the difference is between be true for and be true of? The following is my understanding of the two expressions, am I right?

In sentence 1, the students don't include the teachers, so we use be true for;
In sentence 2, the northwest includes Cumbria, so we use be true of.

Hello, Tdol and Naamplao,
You both agree with me about the difference between "be true of" and "be true for" I stated above. But now I've come across another sentence (the underlined below) that seems not to fit in with my judgement. I'd like you to help me again. Thanks.

OALD6, lawful:
Lawful tends to be used in technical or literary context. The same is true of the opposites, unlawful and illegal, but illegal is used especially about criminal activities.

[RonBee]

Re:

The same is true of....

The same thing is true in those cases. It's the same as was previously mentioned. The same thing is true in those cases as in those previously mentioned.

~R

[David L.]

The trouble we are having is that what is "correct" English is not always how we express things in casual, everyday speech.
"true of" implies that something has an intrinsic quality,or state, or condition
"true for " means that something about X can be generalized or also applied to Y.
So: say in my experience, lawyers always seem such serious people, even when they are not at work but home relaxing. Say that I have found that accountants are like this also. Then there seems to be some intrinsic personality feature of "seriousness" in people of these two professions. I might then say: "Lawyers are very serious-minded individuals, and that is true of accountants also." (My apologies to lawyers and accountants for this no doubt unfounded observation!)

In the first example you gave, you are not referring to some intrinsic quality of students, that all students are generally in some excitable state most of the time, such that it is a characteristic of students; but that they are feeling excited at the prospect of some coming event. So are the teachers. So, "..and it is true for the teachers also."
In your second example, it is an intrinsic feature of the climate in the northwest that they get a lot of rain. Cumbria is a part of the northwest. So, ..,and that is especially true for (that part of the northwest called) Cumbria."
Compare : The Gobi desert in China receives very little rain throughout the year. In England, this is also true of East Anglia.
With "lawful ", the word is characterized by being mainly used in technical and literary writings. The synonyms of "lawful" tend also be characterized by being mainly used in technical and literary writings. So, "it is also true of the opposites."
However, you will often hear people saying "true for" in both situations, as "true of" to modern ears sounds rather 'correct' and 'formal' when people of just speaking casually.