In reply to:

What do you suppose distinguishes the apparently unalterable ones from the ones which invite dinking?

Perhaps it has to with a perception of the intended recipients. The version tsuwm posted was several cuts above the others I read, its focus on language and the generally more intellectual bent making it much more appealing to me than the others. Perhaps the person who forwarded it to tsuwm perceived that modifying its content in such a manner would increase its impact. Or perhaps I'm a gibbering loon.