Well, after looking at a Cricket PRL this is what I found:
SID 4121 (Sprint in Denver) is not in the PRL.
SID 6499 (Nex-Tech Wireless - Sprint Affiliate), which is the coverage to the East of Denver following I-70 to Kansas is in the PRL.
So, it looks like Cricket probably thought their network was as good or greater than Sprint's in Denver, and stripped the Sprint SID to alleviate in-market roaming. However, this sucks because in the process, they strip Cheyenne out because it uses the same SID as Denver.
Can't say I'm happy, but what's a man to do.