@thenomain
It's about the derivation more or less, and whether a similarity can be proven as a 'unique point of similarity'. You can look at VtM and go 'Oh, yes, they took <X> concept from Anne Rice' but you can also look at it and go 'And they did <Y> change/spin on it' with a lot of things. Which ends up pushing it less into the realm of infringement and more into the realm of inspiration and derivation.
The Sacred Core, which links all vampires back to the first vampire Akasha, is obviously the origin of the Generation mechanic; but the Generation mechanic is changed enough that it's derivative of the concept and is not close enough to a 1-for-1 comparative point, and probably wouldn't hold up to scrutiny in that manner in an IP lawsuit. Many of VtM to Anne Rice's comparisons are like that.
This roughly explains why Sony settled out of court; likely there were enough unique points to actually go to court (specifically regarding the Love of Monsters story which is comparable to Underworld's first movie story), and so a prolonged court battle would prevent continued development of the franchise, and so they settled out of court for an undisclosed sum... and you can see in the next set of Underworld movies where they hewed further away from things that could be pointed out as 'unique points of similarity'.
I'm sure Anne Rice could've sued, but there are likely much fewer points of 'unique similarity,' and so it wouldn't have been worth the time to do so. There's also a lot less money to be gotten from an RPG company versus, say, a movie company 'stealing' ideas from VtM. From what I recall, the VtM lawsuit was also pretty flimsy, but the biggest issue was a pretty good comparison to a VtM story The Love of Monsters, as well as a number of terminology and 'setting' choices that, while probably not intentional (like the use of the word 'abomination' used when Viktor is told about the vampire-werewolf hybrid), were enough to go on to actual court.