Jyhad, by the original design, has no hard card limits. It does, however, have a lot of limiting that occurs as the result of the rules. The primary agent is, of course, the concept of unique cards. Without it, you could end up with something like the following:
Crypt: Nik (x10)
Angel (x10)
Library: Ivory Bow (x15)
Warzone Hunting Ground (x5)
Mr. Winthrop (x10)
Flash (x20)
Sideslip (x10)
Effective Management (x10)
Blood Doll (x10)
It's not the best possible such deck (I don't feel like really working one out), but you get the idea. Also, the fact that you can't play a given action modifier or reaction more than once per action has a similar effect (plus the bonding, conditioning, threats restriction). "Well, lets see, that's 8 Threats for +16 bleed, but my hand is jammed with stealth so I have to stop now. Jeez, I only got to use up 4 Lost in Crowds. Guess I'll have to use Deal With the Devil next round."
Jyhad's relative success in making a limit-free system doesn't lie necessarily in the perfect balancing of cards in a way that renders even mixtures the most powerful, but in "soft" card limits. The game doesn't ban excessive use of a few cards, but the system acts to impose the cutoffs that other games introduce explicitly. In the few cases that the system doesn't provide an internal check, abuses are still possible (e.g. KRC decks).
Such a system, I believe, is superior to hard card limits, as it allows real freedom in deck design. No "I wish I could put in just one more of these." It's still essentially a matter of increasing returns, though. Instead of card limits providing the cutoffs at the ends, competition of cards with each other for a limited number of positions within the game does the restricting. When building a generic S&B deck, a primary concern is "how much S&B can I include before my hand will start jamming?" Very similar to "how many 'pump up white' cards can I put in my deck before I hit the card limits?" Admittedly, though, the Jyhad system provides for a much more intricate and interesting balance between cards than does Magic's simple 4cl. Imposing other restrictions on Jyhad (such as tourny rules) isn't changing the nature of the game so much as admitting that the internal card-limiting isn't working perfectly and needs some explicit supplementing.
I think that rules-based limiting of cards is probably the best way to go with CCG's, as truly eliminating card limiting removes an essential aspect of the game. In trying to build an effective deck, one pushes the envelope of the card limits. If there are no limits, building a deck becomes simply an effort to make something interesting to play. Which is by no means a bad thing, it's simply not like curent CCG's. It would be more like SJG's original _Illuminati_ but with added personal flavor. I would very much like to see such a game. It would make deck building non-competetive, though, so it would be a different type of game. As mentioned in the original post,
-> Deck construction [is] the most constant element in different CCGs
Well, I think I'm done babbling for now. I'm not sure if I ever really made a point, but hopefully I brought up some interesting ideas.
For more information on this topic, see Curt Adam's article on the Theory of Card Limits in CCGs.