There is a huge difference from a player's perspective. It does not mean that a coach does not deserve credit for keeping signed recruits (he does), but there is a really big difference.
When a junior who had just given a verbal re-opens his recruitment on a coaching change, he has full Spring, Summer, and Fall (not to mention potentially Winter and early Spring) to solicit recruiting requests, recruiting input, schedule official and unofficial visits, compare schools and go through full recruiting cycle. Furthermore, pretty much all schools still have available scholarships. This is pretty much what the vast majority of all recruits goes through, the same what, for example, Liddell, Okoro, and lesser recruits will go through coming up, despite personal preferences.
When a signed senior faces a coaching change, and a decision to re-open his recruitment after a coaching change, not only does he have to ask out of LOI and wait for his release (a decision that really "burns" significant time, more than getting denied), but he really faces a tough timeline, really just a few days to make decision with schools already having completed most of their recruiting, with many less openings/opportunities, tremendous time pressure to make contacts, take visits, and make an informed decision. Furthermore, once you re-open and get an LOI release (again, schools will have to wait for that release in order to recruit you), you pretty much have strained the relationship with the existing school, taking that option away, which has great risk. Especially if you are not a top recruit, but a 100+ recruit like Frazier. The decision to re-open a recruitment for a signed recruit is really a lot tougher, has many risks, and is a much more difficult decision.