JoeNotCharles
First Post
While that is a good point, we routinely allow many non ubiquitous sources like dragon, the power books etc. This is wizard's business model - the more you buy, the more options you get. I dont really like it, but it is what it is.
The difference is that all these options are supposed to be roughly balanced. Backgrounds and themes are the only things I'm aware of where a player who takes them just has something extra that others don't, as opposed to more options of what to take in a given slot.
For Backgrounds it's just a couple of extra points on a skill, not too overpowering. But for Themes, if I understand it right somebody who takes a theme has a whole extra encounter power that people without themes don't. So as soon as we allow themes, we require everyone to take a theme in order to keep up.
For backgrounds, we have our own Regional Benefits for people who only have PHB1. For themes, if we allow them we'd want to write up some setting-specific themes and publish them on the wiki so that people who don't have any of the official books that describe themes will still have some to take.