Like many people, I've played and really liked I Wanna Be The Guy. Over the years since it was released, new indie games were released. Games like VVVVVV and Super Meat Boy. Games that, frankly, had a better respawn system than IWBTG.
Now, what are the problems with the respawn system of IWBTG? There are two main problems. The first problem is that it takes time. It slows down gameplay quite a bit. This would be okay if deaths were infrequent, but in IWBTG, they are not.
Another problem is that it disrupts the music. The Ghost & Goblins part is one of the best examples on why this is a bad thing. The Monty on the Run segment is also a good example, because I really like that song.

I could argue further, but, to be honest, I think few people would agree that this would be a good feature to have. It could be added to Option, like "Fast Respawn" or something like that. An example from Super Meat Boy how it could work in practice (Note, it's not my video):
http://www.youtube.com/watch?v=2FwcOP3dI3oIf someone added this, I would be much more likely to replay IWBTG.

Would this be hard to program? I have no idea, but it really would be a great addition to the game.