Much as I don't want Google to shutdown Reader (though I'm also relying on the http://www.reederapp.com author sorting out another back-end), I would suggest that the number of people signing the petition is going to be <= the number of people currently using Reader.
And Google have decided that number's not high enough for them to keep it around.
As much as I used Reader (every day, multiple times a day), it was obvious that Google didn't care, because it is broken as hell sometimes. I just never found a suitable alternative. Now I have to.
I signed something there and got a ton of emails about unrelated crap I didn't ask for or care about. That was not recently so things may have changed but I will never use the site again.
And Google have decided that number's not high enough for them to keep it around.