Point is, though, how useful is decimate in its original sense? How often do you actually need to say "take out one in every 10" as opposed to every 5, or 20? You may not like the amended usage, but it probably has a broader and more useful communicative function.
InSearch - every period in history has people bemoaning language change, as if they've just emerged from a Golden Age into A World of Decay.
John Cheke in the C16th:
I am of this opinion that our own tung should be written cleane and pure, unmixt and unmangeled with borowing of other tunges; wherein if we take not heed by tiim, ever borowing and never paying, she shall be fain to keep her house as bankrupt.
For then doth our tung naturallie and praisablie utter her meaning when she boroweth no counterfeitness of other tunges to attire herself withall, but useth plainlie her own, with such shift as nature, craft, experiens and following of other excellent [writers] doth lead her unto... This I say not for reproof of you. . . but for miin own defense, who might be counted overstraight [too strictly] a deemer of things [prescriptive], if I gave not thys accoumpt to you, my freend and wiis, of mi marring this your handiwork.