Brilliant Filmmaking
I don't know how many people who have watched this movie are aware of this, but most of it was shot on a camcorder, which explains its low-resolution look. However, there are two aspects of this that support its use.
First, is the artistic intent. Since this was shot on a camcorder (Canon XL1 DV), this gives the film a gritty, grimy, almost nightmare-like look to it, which perfectly suits the film's post-apocalyptic nature. Now the last few minutes of it was shot on traditional 35mm film, and if you've ever watched this on Blu-ray or an HD channel, there's quite a disparity in look. The ending looks gorgeous since it was shot on film and implies that the apocalypse is over and there is clarity, beauty, and hope in the world again.
Second, is the practical intent. Since Danny Boyle and crew were using a camcorder, this made it very practical and easy to shoot in London for the scenes where Jim is walking around the deserted streets. There was a very limited window of time to shoot every day, and setting up the camcorder made it much easier and practical than a film camera.
I don't know if this movie is ever used as a model for filmmaking in film schools, but if it isn't, I feel it should be, to teach aspiring filmmakers that budget isn't everything and being creative with your limitations can go a long way.