I've never worked at a bike shop, but I've worked high-end retail - I would assume that it's similar, but I'll definitely admit that the places that I worked at warranted favorable terms from many of the vendors.
That said, I've seen it go both ways - it really depends. For a straight-up MSRP reduction for an ongoing model, it was pretty common to have the cost to our back stock adjusted for the next order/invoice.
While we didn't exactly have model years, but there were iterations/generations. Sometimes the pricing on discontinued stuff was adjusted, particularly if we had more than two or three in the stock room. If we were just sitting on a floor demo, why bother? Sell it for more than cost and get on with it. Other times, if we didn't have much by way of back stock, vendors would offer really favorable pricing to entice us to buy some more and then blow them out.
At the end of the day, it was all about balance - it's nice for retailers to have stock on-hand so that they can close a sale quickly (for customers, being able to walk out with something can often tip the scales in favor of making the purchase); vendors don't want to discourage that kind of commitment, so being able to offer some kind of an adjustment when we got stuck with inventory was appreciated.