Henry , XP is just started picking up now , becuase of it's inherent advantages. Like
Java has got inbuilt security through Sand Box , that way XP comes with tremendously lightweight package , ideas where Many heavyweight processes are proved ineffective. Rather thay have made Programmer , whom i consider " an ARTIST " into Documentation clarke. though documentation is imporatant , too much of it will hamper the progress of the project & sap the entusiasm & creativity of Progammer. XP is hammering n those areas only.
As Mr. Kent Beck has proposed in his book : " I am not proposing any new thing here. Everything was available previously." Now , people are understaning advantages offered by Xp. It is still evolving. it will be growing.
Regarding you quesion on applicasbility of XP to larger group, just read this discusssion
thread here. Mr, Fowler & Mr. Chet has explained about that.
I hope this is useful.
SHAILESH.