I agree with you Martenkay. It wouldn't be that hard to implement.
Within certain sensible time frames (up to 1 month or 3 weeks away from race day when the numbers are despactched) it would not be difficult to allow athletes to withdraw and receive a refund or race credit and then allow another athlete to enter. This happens in some triathlon races. The refund diminishes closer to race day and the race either re-opens entries or contacts people from a waiting list. I don't think this is necessarily possible for very, very large races (VLM mentioned above) but certainly think it would be feasible for more than those which offer such a policy at the moment. It isn't that hard to permit transfers either.
I don't think it's the same as no quibble refunds in retail setting though, and think that's not a strong comparison.
Equally, I don't think it's the same as Seren's no refunds for swimming lessons or horse riding lessons at short notice though. The examples Seren cites are a shorter notice issue and those services will perish quicker (ie the place cannot be filled/sold on from notice given that morning), for larger races that sell out very quickly, people may know they can't race months in advance.
I have certainly worked with races who implement such a policy and it provides opportunities to make MORE money (based on the diminishing refund or that refund being a race credit in some cases and not cash), the race then sells the place again and the admin involved doesn't necessarily cost out to the money charged in the fee to withdraw.
Athletes swap numbers anyway and it would stop this happening. This is a health and safety issue, when you enter a race you supply certain information with the medical team keep on hand should you be injured - they will look you up via your race number. If that race number isn't you, unless you've filled out the medical info on the back, they have no idea about you, who you are and if you have any medical conditions they need to be aware of. I think allowing athletes to withdraw or transfer is a good move.
Sadly, it's down to the race and, as Wilkie quite rightly says, if they don't want to do it, they don't have to. We just have to read and understand their terms and conditions/refund policy.
Like Wilkie and everyone else, I pay my money and I make my choice but I do hold races like Sodbury Slog, Beachy Head Marathon, TriBristol, One Step Beyond events, Pacesetter events in higher regard for having these refund and transfer policies in place. Even the Ironman brand has implemented a transfer policy.