Yes, we are making such an assumption--because it's reality. They can fly them to other cities, the pool of recipients is large. It might not be someone at the top of the list but there will be someone.
It's not reality. The absolute truth---and I have personal knowledge, is that geography matters. There is only a very short time period in which to harvest organs, perform all of the testing, which is not just genetic testing but also includes screening for a variety of diseases which can be transmitted by transplant and/or blood donation and transporting the organs to wherever the donor is. Sometimes there is a bigger cushion of time: the donor whose family has agreed to the donation is brain dead but the body can be kept alive while testing is being performed and the best match can be found and transportation is arranged. This is the case with hearts as at this time, only 'beating hearts' are transplanted. The time frame here is still short-- hours and not days. Not every hospital is equipped and appropriately licensed to perform the appropriate testing--a brain dead person may not be at a hospital where the appropriate testing can be performed so blood samples must be collected and transported to an appropriate testing facility. These facilities are very tightly regulated. Not ever potential recipient is within the geographic distance that can be managed within the time frame.
Throw in that families can hold up the process as they come to grips with the death of their much loved family member and sometimes will challenge the donation, even if the donor has signed a card. This all takes very valuable time. It is extremely generous of families to be able to come to grips with all of the issues and agree to the donation at such a very vulnerable time, in a very short time frame.
Matches also need to be not just for tissue type but also size. A child requiring a transplant needs a small organ. A large adult requires a larger heart, not one from a child.
It's not as simple as we'd like to think.