The reason for the delay is primarily to avoid Audi's newest entrants from getting lost in the ether of year-end sales drives, and thus allowing all three vehicles to be marketed as 2010 models, which were originally destined for sale in the third quarter of 2008.
Although we haven't seen the Q5, meant to compete with BMW's X3 and Mercedes' upcoming GLK, it's been well known that the new cute 'ute has been under development for some time, finding a home atop the VW Tiguan platform. The diesel Q7 will be arriving around the same time, and will come to market packing a three-liter turbo-diesel V6, producing 230 HP and 400 lb.-ft. of torque. Since the new engine will be 50-state compliant, it's "just a matter of formality," according to Audi's U.S. head Johan de Nysschen, that the oilburner will find its way into the A4, A6 and A8 models of the future.
All three vehicles, including the 280 HP V6 hybrid-equipped Q7, are all likely to be revealed in Detroit in 2009.
[Source: Automotive News – Sub. Req.]