I have to say those are the best tutorials (on that level) that I've come across... as others have mentioned, they get the information across without being too textbook-like, and give you more than just the basics of each subject, which IMO is really very necessary.
I prefer the ASCII-art to diagrams (it's faster loading and like you said, more simplistic, plus, it gives a copy-paste ability that may in some cases be helpful. Maybe I'm too used to IRC-type places though...).
I find it relatively smooth-scrolling on linux (FireFox v.1.0.7 on linux-2.6.12-gentoo-r6), but I think it's a good use of the static background.