Patron Power Pools are significantly different than the Epic Power Pools in City of Heroes. In City of Heroes, you automatically get access to Epic Power Pools at level 41. With City of Villains however, the access to these power pools must be earned. They are called Patron Power Pools because you choose one of the four Arachnos Patrons to learn from, but just like City of Heroes, you are restricted to only one Patron Power Pool. This makes sense of course, since you can't follow two masters. Each Patron has their own storyline as well, which makes obtaining the powers more interesting as well.
Another important thing to note is that your villain powerset determines what powers are available in a given Patron Power. For example, Stalkers get one set of powers from their Patron, but Masterminds get another set. This is a change from City of Heroes, where everyone gets the same thing. The choice of a Patron is a very important decision, because you can NEVER change your Patron - not even with a Power Respecification. As you can see, its very important that you choose the right Patron for your villain.