Actually, that's exactly what it does... over time. Where exactly do you think our language, as it exists today, came from?
ex:
"Ther nas no man no wher so vertuous" ("There never was no man nowhere so virtuous")
"He nevere yet no vileynye ne sayde / In all his lyf unto no maner wight" ("He never yet no vileness didn't say / In all his life to no manner of man").
The modern English language (written and spoken) has been in constant flux for the last 600+ years. What was once required is now antiquated, and what was once verboten is now required.
At this moment in time, double negatives are frowned upon. However, that may change in the future, and it's possible that irregardless is the start of a new set of changes in the language.
It's worth noting that neither of your examples has a double negative. Triple negative (the second possibly quadruple), sure, but not double.
> At this moment in time, double negatives are frowned upon.
I don't know that there's really a shift in time with the double negative, its a stylistic rule, and, much like the Pirate Code, stylistic rules in English are more what you'd call guidelines than actual rules.
Or, looked at another way, more like training wheels.
Nowher so bisy a man as he ther nas [0] (Nowhere so busy a man as he there none)
[0] http://www.bartleby.com/40/0102.html line 321
Irregardless, it's not about being grammatically correct, but being socially accepted and understood; just like slang and broken grammar that develops in subcultures, it ain't no goin anywhere!