That's not clear from the text.
After this basic game, two further games released eighteen months apart will allow the players to progress and explore the universe first as Rogue Traders and alien pirates, and eventually experienced players will be able to roleplay the devastating warriors of the Adeptus Astartes Deathwatch.
The implication is advancement, from a basic set, to more experienced set.
Players will be able to progress from one system to the next, as they gain experience and a measure of understanding of the vastly detailed universe of Warhammer 40,000.
This statement of progression seems to conflict with the next one. Are they saying the player gains XP as well? (Be an interesting idea) Or they are just supposed to become more familiar with the setting. Also it implies that each book uses a different but related system.
Each of the games will consist of a core rulebook accompanied by regular releases of sourcebooks and adventures.
By Core book do they mean stand alone, or is it more like Basic D&D, Expert and Immortal (remember them?), where one book builds on the previous one, but all are 'core'.