For some reason, people who vote on www.startrek.com
love Voyager. I think among casual fans "Voyager" is very popular because its definitely the kind of show you can dip into easily and get your fair share of boobs and action of the week.
Frankly the results of those polls are often a total joke, apparently the season finale of "Voyager" gave people the most closure. LOL WUT, way to not use your brains voters ;-)
It might be that Voyager does well there because Voyager fans are more comfortable in that environment, not because they are "casual" fans. Here, it is a sport to put Voyager down whenever possible.
All polls on the internet are a joke, even the ones on the TrekBBS. However, it's always a kick when Janeway or Voyager comes out on top.