With regard to the stretching - I've had a back problem in the past and certainly core strengthening along with yoga at the end of the workout has improved my back 90-95%. It's been an amazing thing.
However, with respect to stretching before, yeah - it all started with a big study in the military where they followed thousands of recruits, some of whom stretched prior to their daily exercise and some who did not. There was no difference in injury rates. Further studies showed that powerlifters who did traditional stretches prior to their lifts ended up lifting less.
http://sportsmedicine.about.com/cs/f.../aa022102a.htm