In reference to the September 20, 2011 Banned and Restricted Announcement.
Before Pro Tour Philadelphia, the DCI's stated guideline for the Modern format was to avoid having decks that consistently win the game on turn three. With the results of the Pro Tour in, we are tweaking that goal to not having top-tier decks that consistently win on turn three (or earlier). We also have the goal of maintaining a diverse format.
Seeing the results, these still seem like reasonable goals. The Pro Tour is the highest level of competition, and the best deckbuilders in the world are likely to find the fastest and strongest decks. Many found blazingly fast decks. However, the winning deck could not deliver 20 damage (or equivalent) in less than four turns, and the second-place deck could very rarely do that either. This shows that the format has the potential to meet the initial vision, but it is not there yet.
Blazing Shoal decks exile cards with converted mana cost of at least 9 to deliver turn-two and turn-three kills using the infect mechanic (usually with Inkmoth Nexus or Blighted Agent). While this is exciting the first time, Blazing Shoal delivers that same quick kill too consistently.
Rite of Flame
This was primarily used in combination decks to deliver very quick wins. While Jeremy Neeman did not make the Top 8 of the tournament, his Modern deck won nine out of ten matches, and did so with some extremely quick kills.
Ponder and Preordain
A large number of blue-red combination decks kept the field less diverse. One thing that made them so efficient was the cards that would find their combinations. Ponder and Preordain were the most widely used of those cards. Banning these should make those combination decks somewhat less efficient without removing the possibility of playing them.
The threat of facing decks which could generate fifteen or more mana each turn starting on turn four kept a lot of different decks out of the tournament, greatly reducing the diversity. There are alternatives for people who wish to play mana-ramp decks, but they do not appear to be as crushing.
Green Sun's Zenith
On turn one, this can give the acceleration of a Llanowar Elves by getting a Dryad Arbor. On later turns, it can get a large creature or a one-of "toolbox" creature such as Gaddock Teeg. While this is interesting, it is also too efficient. If one intends to build a deck that has turn-one accelerants, Green Sun's Zenith is a great choice. If one wants to more access to utility green creatures, Green Sun's Zenith is a great choice. If one wants to more reliably get a large green creature, such as a Primeval Titan, onto the battlefield, Green Sun's Zenith is a great choice. However, this ends up with fewer different decks being played in practice, as Green Sun's Zenith is such a good choice that there are fewer green decks that do anything else. The DCI hopes that banning Green Sun's Zenith increases diversity among Modern green decks.
For the past year, no cards have been banned in Extended. The outcome was that the best Standard decks over the preceding years, such as Caw-Blade and Faeries, were the best decks in Extended. Many people who would otherwise enjoy Extended did not enjoy that environment. To avoid repeating this, the DCI is banning the cards that have been most played in the most successful Standard and Extended decks over the past three years. For reasons similar to why these cards were banned in other formats, the DCI is banning them in Extended.
Mental Misstep is banned.
Force of Will has long been thought of as a card that helps keep combination decks in check in Legacy and Vintage. However, it doesn't directly help decks that aren't playing blue. One idea that was floated was creating a similar card that could be played in nonblue decks. When Phyrexian mana was designed, it was an opportunity to create such a card. R&D wanted a card that could help fight combination decks, and could also fight blue decks by countering cards such as Brainstorm. Clearly printing a card like this has a lot of risk, but there is also the potential for helping the format a lot. The risk is mitigated, because if it turns out poorly, the DCI can ban the card.
Unfortunately, it turned out poorly. Looking at high-level tournaments, instead of results having blue and nonblue decks playing Mental Misstep, there are more blue decks than ever. The DCI is banning Mental Misstep, with the hopes of restoring the more diverse metagame that existed prior to the printing of Mental Misstep.
Fact or Fiction is no longer restricted.
While the Vintage metagame is healthy, the DCI is still interested in occasionally unbanning some cards. That allows us to see if the metagame would be even more diverse with these cards allowed. Fact or Fiction was too powerful at one time, but that was when Mana Drain decks were at the top of the Metagame. They still are very good, but the DCI believes unrestricting Fact or Fiction is a reasonable risk to take to increase metagame diversity.