How could he and we all know why,including Peter Gade himself. And why do you think Peter extended a personal invitation to Lin Dan and no one else for his farewell match in addition to hosting him at his home with his favourite red wine. As his only and most distinguished guest for his farewell party, don't expect Lin Dan to 'whack' the host, do you? Not to mention during Lin Dan's long vacation, I think it unlikely he could display that kind of devastating form even if he wanted to but nevertheless still enough to do the job nicely.
Even Lee CW has to admit there is only one Lin Dan. To be frank, Lee CW benefited the most from having Lin Dan as his perennial archrival despite losing practically all the major titles to him; that's how Lee CW becomes so good and ,of course, Lin Dan benefited too from having him as his perpetual number one opponent, it cuts both ways. Similarly to a lesser extent Lee Hyun Il who called Lin Dan the perfect shuttler. Conversely, many 'suffered' during Lin Dan's era, notably Taufik, the most perhaps apart from PG.
interesting to see the change in style for Lin Dan over the years. in recent times, his is faster and much more deceptive in his movement. it is almost impossible to read what he is going to before he touches the shuttle. the variation in both stroke preparation and execution is just incredible. truly a master.