It's true that a lot could have changed since the previous investment round, but isn't that often the case in venture capital funding? Paying a different price

It's true that a lot could have changed since the previous investment round, but isn't that often the case in venture capital funding? Paying a different price for one person's equity changes the valuation for everyone as the new market rate. This can be bad for an individual (could be sold for higher on private market) but also good (prevents someone else from selling at a major discount). Companies want to control valuation much more closely than that, so valuation is pegged to investment or some other major event. Whether that's a good way to do things would be a nice discussion topic, but that's not the same as saying uber in particular is playing hardball. A little bit of research would reveal that it's standard practice.