You can get them on vinyl too, or on 78s if you want to be really authentic (the recordings were made in the 1920s), but the CD box collects all of them. This is a case where hearing the music is much more important than worrying about the format. The Hot Fives and Hot Sevens are Armstrong's best recordings, and his most important contribution to music. Who cares if the easiest way to hear them is to buy compilation CDs?
-- Ian