I haven't done any experiments (mainly because I don't, and won't, grow any control veggies to compare against), but I really think that veggies grown organically keep better than those subjected to chemicals. Even so, I know some of the things I store won't make it in storage. I keep a watchful eye on what's in the cellar - using most things in a timely manner, and taking action when there's something that could damage the rest (one bad apple really can spoil the whole bunch).
I do have one dilemma to which I've given a lot of thought. When things are reaching the limit of their storage life, I used to think I should use up the ones going bad first. But that meant I was always getting the worst of the bunch, and I don't like that. If I were shopping at a store, I certainly wouldn't pick the worst veggies I could find, so why should I do that in my cellar? So now I choose the best when shopping my cellar. I do the same the next time I go after something, knowing once again that I'm getting the best of what's there, until all that's left is better going to the chickens or into the compost. I know not everything will make it no matter what I do, and I'm so much happier knowing we're getting the best, every time.
By the way, as I type I'm snacking on a fresh zucchini muffin as the snow starts to fall once again. By letting the last of the summer's crop grow big and then storing them, I really can be eating home-grown zucchini at Christmas time.