There is (there's) vs.There are

What are the roots of the creeping usage of "there's" for both singular and plural predicates? (This seems to be more common in spoken English.) I have 2 theories. Perhaps it is because spoken communication our society is becoming less formal by the day. Or perhaps it is a reflection of speakers of other languages having increasing contact with native English speakers. I am aware of German "es gibt" and Spanish "hay" constructions. Please comment.

3/06/14 I ran a couple of Google Ngrams and was surprised to find a greater rise in the use of "there's" in English fiction than in general English language books, since the turn of the century. This would seem to support my contention that informality is behind the shift.

The contraction "there're" does get used but it seems entirely dependent on regional dialects and it isn't so much a strict contraction as the "e" and "a" can sound merged together when a fluent speaker is speaking quickly. Locally, I hear what would be more accurately be transcribed as "ther're".

I am a little hesitant to accept your premise that "there's" is becoming more common than "there're". Even if it was true, I suspect it would be regional.

But, as John Lawler notes in the comments:

There doesn't need to be any number agreement for the existential construction. In German, for instance, one says Es gibt 'It gives', and the noun that follows is either singular or plural without needing agreement. That's the reason it's disposable. The reason it's spreading is that it's a contraction, which makes it easier and popular, and there's no good contraction for there are. You can write there're, but how do you pronounce it? Contractions are created by speech, and only reluctantly used in writing. One hears There's some people here and everybody understands. That's all.

Some dialects have little troubling pronouncing "there're" and the rest would fully understand "There's some people here."