There are a lot of ways of classifying roses; by their heritage or presumed genetic makeup, by when they were produced, by what size and shape they are and how they might best be used. Any rose classification system that attempts to express all the useful distinctions rosarians make about roses is bound to muddle together these concepts.
To a person new to roses, the number of classes is dizzying. A sort of 'person on the street' idea of rose classes might be; cutting roses, shrubs, miniatures, climbers. Or some method closely akin to this. A rosarian will rightly want to know "is it a wichuriana climber or a multiflora climber or a kordesii climber?" Because these things can affect the care and expectations of the rose.
The WFRS notion of a kind of heirarchical system with old and new making up the first heirarchical level has been adapted. Instead of using 'new,' we have broken up the more highly bred classes of roses in a way that more nearly parallels the 'person on the street' notion of roses classes. This has two poerful advantages: First, of immediate recognizability- novices and experts can start out using the same categories and language; and second, of not having to reinterpret 'old' and 'new' every couple of decades. For all that is new becomes old.
This said, we have pretty much stuck with WFRS categories, though we will occasionally use the terms Hybrid Tea or Floribunda because they seem more compact, melifluous, and recognizable.
Some of these categories are very narrow. Albas, Gallicas, and Damasks have quite a lot of similarities with oher roses in their classes and roses in the classes are frequently easy to distinguish from those of other classes. Roses in more highly bred classes such as Modern Shrubs will display quite a wide variety in their characteristics. Still, these groups are reasonably helpful in locating roses with similar characteristics.