I noticed the same phenomenon last night, sort of, which shows how the language gets a little bent in the speaking of it. It may be regional, but I'll bet it's pretty widespread tongue laziness. This example doesn't change the meaning, but certainly alters the production of sound (like your 'disappearing' "a" sound).
I was visiting my sister last night when my nephew returned from basketball practice at dinnertime. The brief snippet of conversation on point was:
Sis: Did you eat yet? = Didja eat yet? = Djeetyet?
Nephew: No, did you? = No, didjoo? = No, Djoo?
I'm sure some linguists would point out that all of the phonemes which are crucial to the conveyance of meaning are present in these utterances, but certainly enough of them had been dropped or altered so that it caught my ear.
Interestingly, I also note that the final "t" in my sister's question was altered from a aspirated fricative (I hope that's right) to a full glottal stop (ditto).
Thanks for pointing out the Armstrong thing; I'll keep listening for other examples, especially where meaning is altered by delivery. Fascinating.
Ron.
