EDIT: after reading the post above, I'd like to add that there may even be regional differences with all of this, so let me state this is based on my own experience.
No, not really IMHO - much more complicated. The first article (I only skimmed) seemed pretty good, the second was prolly a Japanese person trying to codify it :-) Here's a foreigner's attempt to explain them, based on how I use them (and I'm focusing on "thank you", not all the other meanings):
"su(mi)masen" means literally "it isn't finished" - meaning, I feel the need to repay you. "Arigato" is more literally "thank you", but is more of a "ending, cutting off" feeling. Neither is more polite than the other, just used in different circumstances. Which makes it terribly nuanced.
On the street, in the shops, normal life: "sumasen", which ends up being a lot like "thanks" that we are originally discussing. Why not "arigato"? I think because it would sound really abrupt, cut off ("curt" often used in literature).
Family member passes the salt - "arigato". No need to make a fuss, just a "thanks"
Someone close to the family has given you a gift, done something special: "Arigato gozaimasu!" (with 20 or more little sumasens thrown in) - I couldn't possibly return such a special effort (even though I'll deliver a returning gift to your house tomorrow) so it would be insulting to imply I'm going to.
You get the idea of how nuanced and confusing it can be. You just have to learn it naturally, I think.
