Dear Erik ,
you did mentioned todays we can get many LEDs for the price of an motor , here a simple motor costs about $1 and for this price you can get 40 standard 5mm LEDs atmost , and with this quantity of LEDs a 2x20 display could be built ! Bob's sample project demonstrates a 7*30 array of LEDs. such a matrix Display will need 240 LEDs which cost about $6 , and this will need a big PCB to be made and making a Cylindrical PCB is a Real pain (atleast in my mind) so adding the PCB cost completely eliminates the cost benefit.
Also reading the info i've gaved in the previuos reply shows the benefits of desiging such a display over the matrix ones.(of course i'm not comparing these two in a manner of desiging a commercial and fail-safe display)
for a project this type of display makes more sense .

Best Regards :
Farshid J.H.