I actually did play around with having just the set numbers; at the time I didn't go with it because it didn't fill out the whole screen and looked dumb, besides having 19 columns to deal with it. Now the width isn't a problem and we could see what it looks like. I just went with blocks because that's essentially how the formats are defined; no format accepts, say, a base set and excludes the expansions (no standard format, anyhoo). Reflections, Expanded Middle-earth, etc, are not, as far as I can tell, technically part of their block, as far as the block formats were defined at time of release.