What follows is a hypothesis of mine. I'm wondering if there's historical merit for my hypothesis.
It seems the English language has a much bigger change between the documents produced in the early 1800s to those produced in the early 1900s, than the early 1900s documents have until now. For example, in the late 1700s/early 1800s, the letter u was still sometimes represented as v (i.e. as in the US Constitution), but no such changes in the glyphs used to represent the language, nor "structure words" (words critical to language structure, i.e. "is" or "the" or "a"), have occurred in the last hundred years. There have been significant changes in typical vocabulary, but not in language structure.
I suspect that a large reason for this is the spread of mass communication systems, such as office typewriters, Xerox machines, rail transportation, telegraph, and (most recently) computers. My guess is that the reason is that when you have mass communication at the scale these technologies span, standardized language becomes much more important. Consider if the letter u being represented as v (as I pointed to earlier) -- this would be a monumental change which would be unlikely to appear in the modern era, simply because of the number of standards (i.e. ASCII, Unicode, most all information exchange definitions, fonts, most programming language definitions, etc) which would be affected would be enormous. Couple this with the fact that English is already easy for computers to work with (no letters running together (like those which require complicated typesetting systems i.e. Uniscribe), relatively small number of glyphs, no stackable accent marks, etc.), and it seems like major changes to the language itself would be prohibitively expensive in the modern era.
Does any of this make sense, and is there historical justification for it? Or is this my own subjective babble? :)
EDIT: To clarify: I think the typical vocabulary of the language is still going to change (who ever heard of Googling something 15 years ago?), but that the glyphs and structure will not.
EDIT: The reason for the bounty is that at this point th only posted answers have merely been opinions; I'm interested in historical precedent in either direction.