I've seen several folks asking why Apple is keeping around the iPad 2 and not replacing it with the iPad (3rd Generation). To toss my hat into the ring on why, I think it boils down to the chips each device use.
The iPad (3rd Generation) uses the A5X chipset. This was the only device to actually use that chipset, but since it was their top-of-the-line product at a high sales volume, this was acceptable. With the advent of the new 4th Generation iPad with the A6X, this is no longer the case.
By keeping the iPad 2 in circulation, it allows them to continue to use the same A5 chipset found in the new iPad Mini, as well as the iPod Touch (5th Generation) and Apple TV (3rd Generation). This means they can produce the A5 for multiple devices, the A6 for the current flagship iPhone 5, and the A6X as the new flagship iPad (4th Generation). Special chips for the flagships, more common chips for everything else.
TLDR: They probably didn't see a big enough market for the iPad (3rd Generation) to justify making a CPU that would only be used by the one device. Still using the iPad 2 allows them to use the A5 chips they're using in other products.
The iPad (3rd Generation) uses the A5X chipset. This was the only device to actually use that chipset, but since it was their top-of-the-line product at a high sales volume, this was acceptable. With the advent of the new 4th Generation iPad with the A6X, this is no longer the case.
By keeping the iPad 2 in circulation, it allows them to continue to use the same A5 chipset found in the new iPad Mini, as well as the iPod Touch (5th Generation) and Apple TV (3rd Generation). This means they can produce the A5 for multiple devices, the A6 for the current flagship iPhone 5, and the A6X as the new flagship iPad (4th Generation). Special chips for the flagships, more common chips for everything else.
TLDR: They probably didn't see a big enough market for the iPad (3rd Generation) to justify making a CPU that would only be used by the one device. Still using the iPad 2 allows them to use the A5 chips they're using in other products.