This comes from two simple facts. By using this service program you do not have to call the HTTP API's directly, as you can invoke them through simplified calls to Mel's subprocedures. This results into easier coding and about no test requirements as compared to the native API's invocation in a native CGI you would have to build the response HTML string within your RPG program. This would result into the practical impossibility to maintain that coding in the long range. With Mel's service program you are allowed to define your HTML script outside your program, in a source member.
Sections usually contain both text and variables.
This is very similar to the DDS method, with the advantage that there is no level check. The whole of my site is based on this technique. Nuts and bolts of Mel's tecnique are explained in detail in my tutorials. This is why there is no need to attend a class to learn this method. About the easiness and the productivity of it, you may judge by yourself after three days of self training.