Exo,
A CD4017B (or any other regular CMOS chip) will typically supply a current-limited 14mA with a 9V supply, which is well within its ratings. Some a little more, and some a little less.
14mA through an ordinary LED is bright, and through a modern high-brightness LED is dazzling. Haven't you seen those flashing kids shoes?
The current-limiting resistor was calculated to protect the CD4017B with a generous margin, according to the max. ratings on the datasheet.
Elf,
Ignore for a moment that your sight and hearing have built-in automatic gain control. If your eyes and ears weren't logarithmic, and were setup for a sunny day and a loud jet plane nearby, then you would be blind when it is cloudy or nightime, and deaf to someone yelling or talking (or whispering?) in your ear. I'm not talking about selective blindness or deafness (Sorry wife, I didn't see your new dress, and I didn't hear you tell me to take out the garbage).
I built a linear ramp for slow, smooth LED dimming. The LED didn't dim much. Then I made the ramp logarithmic, and it worked well until offset voltage affected the dim microamp current level.