What was the purpose of that? I've used the term "chase cards" on my website. Should I ask Bob?
Based upon somewhat hazy recollections, one possible reason for Wizards not wanting the term "chase card" related to any of their US offerings at that time was possible adverse litigation and law suits.
A short time before the issuance of Planeshift, there was a move by some politicians to go after the many collectible card companies that were making extensive use of chase cards to sell product. For those unaware of the term, it applies to cards that are much rarer, more desirable, and usually much more valuable than "regular" cards. Examples of premium chase cards found in sports offerings included autographed and special foil cards, as well as pieces of equipment or jerseys inbedded in special cards. Some of these cards became so valuable that kids were buying packs of product in search of the chase cards, and were often throwing most everything else away.
With most older collectible card offerings, each card in a set had approximately the same number of copies made. The new offerings purposely made some cards much rarer, and therefore more valuable, than others. Faced with these newer offerings, some lawyers argued the distribution and desirability of these special cards, combined with the method of selling (randomly, and blindly, in a sealed package), constituted gambling. The argument was that these kinds of offerings, where most packs were worth very little, and a few were worth a lot, were, in fact, lotteries (which are supposed to be regulated at the state level) being sold across state lines to minors.
Wizards was soon included because of its unbalanced make-up for many of its products (only one rare to many commons). In particular, Pokemon cards were going crazy and kids were buying packs trying to find the expensive rares (like the original Charizard Foil), then throwing out the commons and uncommons.
Wizards tried to defend itself by claiming that it valued all cards at the same price, and was not influential in making or manipulating secondary market prices for its products. Ironically, this gave a minor legal loophole to anyone making proxy cards that began as a real magic common. Wizards couldn't argue loss of income if someone took a common and made it look more like a rare, since both the common and rare had the same "value" to Wizards, and that value had been paid upon purchase. Furthermore, Wizards couldn't argue that proxies reduced the aftermarket value of its products, because it supposedly was indifferent to aftermarket valuations.
A class action suit against the chase cards was prepared, while lawyers on both sides tried to hammer out behind-the-scenes agreements. The story made it to the pages of the Wall Street Journal. Apparantly Wizards managed to avoid the suit when it was determined that the lead lawyer in the Class action (from NYC or Long Island) belonged to the same firm that represented Wizards (from its west coast office). Combined with Wizards earlier statements (about valuing all cards the same, and not setting individual card prices on the secondary market), they were allowed to continue their unbalanced distributions. I don't know if the suit ultimately died, or whether any out-of-court settlements were ever reached.
But around that time I expect that Wizards was more than a little touchy about any of their offerings being labeled as "chase cards".