To a certain degree you're correct. But it's not exactly the same. With colours you would get larger spans, whereas with numbers you get the immediate feedback. The difference in time is significant for addictive personalities. A second difference is that you don't know the spans, only that they exist, meaning that as the site grows the spans can be upped to keep up with the growing number of users.

Anyway... really like your idea :).

Was going to write something about colouring entire threads or sub-threads as interesting based on the total sum of points or something else compared to everyone else. Would certainly help finding interesting stuff to read in 200+ comment threads. But not too sure how it would work without being invasive.