Not "buying over" because the Accord is still the 2nd best selling sedan behind the Camry, but more people are looking at other cars like the Kia and Hyundai more and giving them a chance.
People are just saying that companies like Toyota and Honda are resting on their names, and playing it safe while other companies are coming out swinging hard.
Look at this, this was sales of mid-size cars from 2002 (or their first year if they were all new cars debuting):
Toyota Camry: 434,000
Honda Accord: 398,980
Ford Taurus (which was still a mid size car in 2002 and didn't become a full size car until the Fusion arrived): 332,690
Nissan Altima: 202,822
Chevy Malibu: 169,377
Mitsubishi Galant: 97,343
VW Passat: 96,142
Subaru Legacy: 85,359
Hyundai Sonata: 68,085
Mazda 626 (was still around in 2002): 40,689
Kia Optima: 26,793
Now look at the sales in 2011
Toyota Camry: 308,510
Nissan Altima: 268,981
Ford Fusion: 248,067
Honda Accord: 235,625
Hyundai Sonata: 225,961
Chevrolet Malibu: 204,808
Kia Optima: 84,590
Subaru Legacy: 42,401
Mazda 6: 35,711
VW Passat: 22,835
Mitsubishi Galant: 15,631
Suzuki Kizashi: 6,942
Kia said in Car and Driver that they would be increasing production to try to keep up with demand.