~quote tree snipped~
Decimate irks me, too. It's one thing to create new meanings and nuances for a word, and another thing to have a word misused until the misuse becomes accepted as an official definition.
Sure, it happens to plenty of words, and I'm lucky if it's the biggest irritation in my day, but I do cringe when I hear it come out of a newscaster's mouth! 
This reflects a major change in how we view language.
Dictionaries are not prescriptive. They were once, when they were the the repository of standard usage, standard spelling and grammatical rules: a tool to try and fix language, give words an absolute definition and usage that was considered the 'pure' and 'correct' use. But language isn't something that can be fixed. It's constantly evolving and changing, and now dictionaries seek to be descriptive instead - they show language as it's being used. Definitions are slipping and changing. Usage is slipping and changing. Dictionaries reflect that. Don't look to a dictionary for a definitive "this is right" ruling. It will describe all the different usages for you, instead.
That's probably been the case for the last century, but we're all still hung up on a fixed definition, fixed spelling and fixed rules. We like order and structure. Language, being the slippery beast it is, doesn't much care for either as long as it gets the meaning across.
Like you, I prefer to use 'decimate' in the old, fixed way, but I acknowledge that the meaning has morphed and changed. Other, similar, changes in words and usage will gradually take on the same level of 'rightness' as the old standard - the misuse of 'lay' where 'lie' should be used (
"Come and lay down beside me," coaxed John is a sentence that makes me shudder) is so widespread, that I don't believe there's a hope of reversing that trend. It will still make me shudder, but eventually it will become the norm and language will have moved on another step in its evolution. Whether that's a forwards or backwards step depends on your point of view.
