Entertainment Weekly AOL has poll results in issue # 670:
The question was "What reason Elvis popularity 25 years after his death". 86.617 votes were submitted, the results were as follows:
54% He's the greatest Rock Singer ever.
23% His immense sex appeal.
17% I don't understand his appeal.
6% The mistery surrounding his death.
Source: ECG / Updated: Sep 5, 2002