It blows my mind that there are still people linking to tutorials that instruct people to use immediate mode in 2011.
Anyway I doubt JOGL does not let you to use buffers, so you can draw in memory and after that draw on screen. Even the Red Book starts with drawing directly on the screen; the double buffer technique is useful for animations ...
For example, I recently prototyped a simple 16x16 tile demo over an 800x600 screen. In immediate mode, that's 1900 tiles on screen at once, and each one demanded 4 calls for tex coords (GL_QUADS) and 4 more for vertex data. That came to 15200 OpenGL calls every single frame, enough to stress my modest hardware. With vertex arrays, buffers or display lists, that could be brought down by orders of magnitude, probably with a dramatic performance boost.
Most people hardware is much better than mine, but my point is that OpenGL immediate mode doesn't scale well even for simple things.