Cut to Arthur's 21st birthday party and investiture as Crown Prince, which if I remember correctly means he will no longer have to have a Regent appointed when his father dies but can assume the throne directly.

That's how I understood it; it just leaves you kind "meh" when Arthur wore the crown he gets in 1x02 already. Gah, such inconsistencies drive me wild.

Which totally explains why Uther is jumping at shadows in a dark room with a sword at the ready.

LOL.