There are many facinations with the 20, and this question has been asked before... here are some that can think of off the top of me noggin...
-inexpensive (relatively)
-able to be personalized (able to be highly modified) its about taking something and making it your own...
-a green alternative (to make that which was old, new again)
-it isnt the statis quo
-it takes a true commitment to want to modify one for maximum performance
-it takes inginuity to deal with some difficult issues
-for me, in my region, it's RARE... REALLY RARE...
-it is a solidly designed folder. (horizontal fold)
-it's steel
-a lot of us dont have 500-1000 dollars to spend on a folder...Up Front 
but can sfford to have the R-20 bleed us over an extended period of time
-R-20 riders are a fun bunch...
-They are too small to get laid on, but when you get off of it, You will get laid HA!
Your question also isnt necessarily about the bike, but it for some it's more about the individual. The EASY way usually isnt the fun way. Some of use need to be challenged. some of us need to express ourselves, Some of us like Jur want to be on the the lil' engine who could. You asked a big question, and I guess all I can give you a lil' answer... -if you dont have one, you wouldnt know...
come check the progress...
http://web.mac.com/phatatude/Green_S...enty_Blog.html
R-20's :
Many ask, few know...