It may also be the Boston way to answer to some fast runners who have been complaining for years that we the "middle-of-the-pack" runners are lowering the quality of BQ (we've all read and commented on those articles). The Boston officials are regaining some control over the "quality" of the runners who will run Boston by giving the faster runners the ability to register early. (Don't forget that for many fast runners, running Boston is an annual tradition.) By doing so, Boston are not responsible if we, the middle-of-the-pack runners cannot register, although we qualified fair and square within the qualifying times they posted.
Regardless of why Boston have decided to implement this new system, I'd rather have them tighten the qualifying times, work my ... off, qualify fair and square, and have the same chance to register than anybody else.