People don't have to upgrade right away even if a newer model comes out. I bought my iPhone 4 in 2010 and I used it for 2 years, then when my 2 year contract was up I upgraded to the iPhone 5. Sure the 4S came out in between then, but I didn't feel the need to upgrade. Once my contract was up and I could get my new phone at a discount, then hey why not?
They kind of did have some reasons for refreshing the iPad late last year. They were moving their whole product line iPod Nano/iPod Touch/iPhone/iPad mini over to the lightning connector and it would be kind of strange if the big daddy top of the line iPad was the only one still using the old 30pin connector. While they could have just updated connector they also threw in an upgraded SoC A6X based on the recently released iPhone 5's A6, but with a more powerful gpu (more cores) at the same price as the previous iPad.
The A6/A6X wasn't available at the time of the iPad 3 release, so now that it was ready they could throw it in as well, plus it added extra value and made the big daddy iPad the most powerful in the iOS line.