That's right Blizzard has announced the end of the current season 4 arenas. However, the arenas will remain open until the release of Wrath of the Lich King as per this note that Nethaera posted in the official forums.
WeÂre currently planning to end the fourth Arena season on October 14, 2008, and as always -- this date could easily change. This Arena Season is only ending in respect to the ladder, meaning we'll be taking a snapshot of the season's ladder and then go through our normal process to determine who is eligible for the end-of-season rewards. This process should take approximately one week. It's very important for players who feel that they may be eligible for the arena-specific title and/or Armored Nether Drake to refrain from transferring their character to another realm between the date outlined above, and when the end-of-season rewards are physically awarded.
Upon the end of this Arena Season, teams and ratings will not be wiped, and will carry forward allowing players to earn points each week and purchase gear until the launch of the expansion (November 13, 2008).