Knuth's original are not really raster fonts, they are vectors but in a format which is not supported in other systems so they have to be mapped to raster fonts before being include e.g. in PDF files. The important difference is that you can customize for which resolution they should be rasterized, so you can get good looking fonts by setting sufficiently high values for your screen and zoom requirements. (Of course this doesn't help if you only get a finished PDF from someone else and for the Type 1 variants it's no longer important anyway.)