According to Valve and this nicely hilarious press release that pokes fun at the company’s track record for its games slipping into the infamous release date triangle, Portal 2 is special for yet another reason:

VALVE ANNOUNCES SHORTEST DELAY IN VALVE HISTORY

Valve today announced that Portal 2 — the sequel to the ground-breaking title that won over 30 game of the year awards, despite missing its original ship date — will now be available the week of April 18th, 2011. This two month slip not only marks the shortest delay in Valve’s proud tradition of delays, it represents the approaching convergence of Valve Time and Real Time. Though this convergence spells doom for humanity, it will not affect the new Portal 2 release date.