I can't imagine Black Crusade being that radically different from the three games that preceded it.
As it happens, Black Crusade differs in numerous ways from the three previous games - FFG (including myself, as I wrote the Psychic Powers and Daemon Weapons sections) took it as an opportunity to make some fairly significant changes to the way the game works. In particular, Black Crusade character advancement is near-freeform, guided by the character's alignment to one or other of the Chaos Gods, replacing the older Career Paths with starting archetypes packages.
To the original poster:
Character advancement in Black Crusade does not impose any sweeping limits on who can buy which advances, skills and talents - any character can buy anything, so long as they meet that individual advance's prerequisites. What differs is that the cost of those advances is determined by the character's current alignment.
All skills, talents and characteristics have one of five alignments - Khorne, Nurgle, Slaanesh, Tzeentch and Unaligned. Every 10 Corruption you gain, you check your alignment. Ignoring Unaligned advances, total the number of advances (skills, talents and characteristics) in each alignment - if you have five more in any alignment than in any one of the others, then you're aligned to that god. When aligned to a particular god, that god's advances are purchased at the cheapest rate, another god's advances are at the middle 'allied' rate (as are Unaligned advances), and the other two are at the most expensive "opposed" rate. So, a Khorne-aligned character treats all Khornate advances as the cheapest, all Unaligned and Nurgle advances as allied, and all Slaanesh and Tzeentch advances as opposed.
I can't give proper page references, as I'm not at home and don't have my book with me - rules references are from my copies of the pre-print manuscripts.