Lushbob, most of them do start out as art projects. There are some that are simply for cash, and those stick out like a sore thumb. Most good decks though were the vision of somebody (art wise).
I meant companies like Ellusionist and Theory11. Obviously, their decks are art pieces (at least most of them are), but they weren't made solely for the purpose of being a display of artwork; they were created to be a deck of cards. If every deck was made solely to be a way to display art, and the idea of actually mass producing them and selling them as a deck was an afterthought, then what would cards be like? Although, of course, companies wouldn't be able to do this; once they designed and sold one deck, they'd create the other decks to sell, rather than to just display art. But it's an interesting concept, I think.
This is interesting because all artists face this dilemma: should I make art for A) art's sake, B) enjoyment's sake, or C) money's sake? Of course these aren't mutually exclusive, but it's definitely an issue that an artist/designer should be aware of.
I'm freely going to admit that the interest in my deck has influenced my decision to make changes (creating the jokers, the back, coming up with a name for the deck). However, this deck is first and foremost a means for me to end my artistic drought (I was an art major, but my day job is in no way artistic at all).
Call me crazy, but I want to create a new deck every year. Would I print and sell them? Of course I could. For me, it's an exhilirating challenge to design a deck, and my life is better because of art.
I can't fault people or companies that make cards solely for profit, because it keeps the market interesting for collectors. Also, you have to have the bad to enjoy the good.