I can't seem to find concrete evidence, but here is what I have found.
The two frequencies listed are center control frequencies for the Merwyn Center sector. 135.575 is listed as being, "High", altitude, while 123.925 is listed as being, "Low Discrete" (altitude). I wonder if the centers load or work, or if cruising altitude, has something to do with it?
All three departures appear to have different steps, or altitude ranges, as aircraft pass different waypoints. The difference between the three really seem to lie in where they go. The Jodub Two heads southeast (below Buckeye MOA), the Rockt One heads northeast (north of that MOA), and the Whitewater Three heads Northwest. There are also time limits for departures, according to the terminall procedure (link below).
Anyone else reading know what altitudes "descrete low" and "high" altitudes actually are? 18k-24 low? 24+ high? etc
Hope that helps!
Here is one place to find the Terminal Procedures:http://126.96.36.199/digital_tpp.asp?ver=0504&eff=4-14-2005&end=5-12-2005