Those unfamiliar with the history of the English Prayer Book tradition and Anglicanism, are probably not familiar with the term "Black letter days". The concept refers to the classification of feasts in the Church Calendar. With the reform of the liturgy in the 16th century, the Church Calendar was heavily revised, with most of the pre-Reformation material scaled back. In the medieval liturgies, each feast day had propers and there existed a complicated system of preference on which day should be celebrated and which had prominence. Cranmer's reforms largely deleted this system. In the Book of Common Prayer, only New Testament Saints (St. Peter, St. Matthew, etc.) and biblical events (Ascension, Christmas, etc.) were retained as proper feasts with their own collects and lessons. These were printed in red in the Calendar, hence the name "red-letter days". Some other post-New Testament saints were retained in the Calendar, but were not provided with propers. These latter days were printed in black and called "black-letter days".
The black-letter days were not celebrated liturgically, nor were they ever intended to be celebrated in that way. They were mostly reintroduced for civil purposes (often times government sessions and other civil things were operating on the Church calendar, hence "Michaelmas term" for schools and etc.). This does not mean that Anglicanism is opposed to celebrating holy days or seasons. However, Anglicanism has set a limit on what can and should be celebrated. The litmus test for Anglicans is the New Testament, only these saints and events are celebrated liturgically because they can be verified as authentic. The problem with post-New Testament saints is the problem of hagiography or the embellishment of the saints' lives due to superstition. The human mind naturally lends towards idolatry, which Cranmer and other Reformers understood well, the tendency is towards the falsification of human lives to satisfy pagan religious sentiments. Often times it has been discovered that saints are complete fabrications and do not even represent a real human being (i.e. St. Christopher).
When one looks at the development of the Anglican tradition in the United States, one learns a great deal about how Anglicanism was practiced in the 18th and 19th centuries. For instance, an unrelated point deals with the Ornaments Rubric. The American Church deleted this rubric, not because chasubles were worn in the Colonies but because no one was wearing a surplice so it seemed unprofitable to reprint a rubric requiring its use. The same can be seen in the Calendar. If one observes the American prayer books, they will find that there are no "black-letter days" in the American prayer books. The black-letter days were not "used" in any functional sense and in the same way that the Ornaments Rubric was deleted so were the black-letter days, which became a problem for the later Tractarians in America.
The question arises, when looking at the American prayer books as to the nature of political commemorations that are observed in both the United States and in England. For instance, the American prayer books provide propers for Thanksgiving and (later) Independence Day. The English Prayer Book provided forms for State Services until Queen Victoria removed them in the 19th century. The difference between these political observances and black-letter days is that political commemorations do not lend to idolatry, whereas black-letter days can if they are not properly conducted.
With the re-introduction of Romanism into our Church via the Oxford Movement, there came an aping towards the saints (which is inherent to Roman superstition and pagan religion). The black-letter days on the Calendar provided an excellent opportunity for the Tractarians to satisfy religious superstition. The problem was that there were no propers for these days in the English Prayer Book (because they are not to be celebrated). The first attempt at reintroducing medieval collects and propers into the Anglican Calendar that I know of was Percy Dearmer's English Liturgy (published in 1903). This really demonstrates the novelty of the concept of commemorating non-biblical saints in Anglicanism.
Modern Anglicanism has complicated things a bit further by commemorating people who are not recognized as "saints" by the "undivided Church" (which it has the right to do). Anglicanism does not have a tradition of canonization (with the exception of King Charles the Martyr who was granted something akin to canonization after his martyrdom). This creates a unique problem when the powers that be hardly consider themselves Christian anymore (and hence the proliferation of questionable characters in the newest sanctoral calendars released by our Protestant Episcopal Church).
The solution? Revert to the classical position of only commemorating biblical saints.