just to prevent a flat if the slick itself desides to spin on the rim. I think if you get them to seal good with some tire glue and use some wheel screws to keep the slick in place you can get away without using tubes, if you have issues with the slick leaking air or other issues then put tubes in it and you wont have to worry about them losing air. I think it may just be the way they design the beads of the tire. Not 100% but thats my guess is they dont trust the slick to seal very good at low psi's and to use tubes to keep air in the slick.