Apple's online storefront includes shipping times that give prospective customers an idea of how long they'll have to wait before an item arrives on their front door. Many Apple products no longer have an estimated ship date and are labeled as being "In Stock". The only products with a ship date are those with limited availability.
In the past, these shipping dates were used to estimate product inventory and guess when new products may be released. Earlier this week, savvy customers noticed the ship dates for the iPhone 4 slipped from 24 hours to 1-3 days. This kicked off a round of speculation that Apple was clearing inventory of the iPhone 4 before the launch of the iPhone 5.
Likely tired of these rampant rumors, Apple has removed these ship dates leaving customers and rumormongers in the dark about product inventory.