Hydraulic lifters are used because they are more forgiving on the rest of the hardware and do not need to be adjusted. You will notice that on certain Hondas and other cars using solid lifters that they have to adjust the valve-lash every-so-many miles as the lifters, cams, and the rest of the valve train wear and begin to have out of spec clearances that create noise and other problems. The reason solid lifters are used for racing is that they do exactly as the cams tell them to do, their is no "slop" associated with them compressing from the hydraulics which can cause a type of valve float during very high rpms and using very aggressive cams. A solid lifter can still be used with even the mildest of cams if you wish, but they are certainly more maintenance.
