I guess to extend Len's explanation a little further- robusta has a very narrow taste/aroma spectrum. There are some minor exceptions to this rule, however generally a robusta grown and processed in Lampung, cups fairly similarly to a robusta from Vietnam, a robusta from Uganda and a robusta from India. Processing methods (washing- drying- polishing) at origin have some impact on the final quality of the bean- but really the differences are not huge.
On the other hand (using an Indonesian coffee example) Arabica from Aceh, vs Mandehling, vs Java, vs Toraja, vs Irian Jaya are all hugely different in their cupping profiles.
Arabica has twice the chromosomes of Robusta- and the species (and various sub-species and hybrids) develop characteristics from soil types, altitude. sunlight hours, rainfall/percipitation, chemical balance in the soil as well as the processing techniques as above.
Len is indeed correct- just because its Arabica does not necessarily mean it will roast well and cup well!