Not entirely true. The 3rd generation shuffle was introduced in March 2009. There seems to be no reason to break out of the current one year cycle, though.
they might just introduce new colors, isn't that what they did several times with the 2nd generation before finally moving on to the 3rd gen at some random time.
then no one liked the 3g's lack of buttons so now the latest 4g shuffle is pretty much the same as the 2nd, which they had already waited a while with. there probably won't be a new model for some time