These tend to be the most powerful cards that will be built into a deck in smaller numbers, if not just as a single card, with the intent of them being the backbone of any decks strategy
Adeline is a powerful 3 drop Human Knight with power equal to your creature count
Pockets Crown rares can be pulled every few hundred packs for free MURs require real investment and real luck
For an idea of the kind of figures these cards fetch at auction, see my article on the most valuable First Edition Pokmon Cards .
Post-May sets (Abyss Eye (Pitch Black) onward) start at the higher 6,000 floor, creating a natural price gap
This not only gives you the pleasure of opening a new pack, and indeed the chance to pull a great rare card, but also starts to fill up your online collection from which you can design your own battle decks