Are you sure you read correctly? I also have Aetna and they definitely cover the band, just the way it's worded may be confusing. Why don't you call an Aetna rep and make sure that it's not covered. It would be wierd if your employer chose to just cover gastric bypass and not gastric banding...
these are what aetna covers - i bolded the band
open or laparoscopic Roux-en-Y gastric bypass (RYGB), open or laparoscopic biliopancreatic diversion (BPD) with or without duodenal switch (DS), or laparoscopic adjustable silicone gastric banding (LASGB)
good luck!