A lot of people think that on imgflip.
I don't think it's true, though.
If people were upvoting users, rather than the meme, then memes by popular users would tend to all have the same amount of upvotes (because their fans would come and upvote all their memes regardless of content). But they don't.
Also, if people were upvoting users, rather than the meme, new users would not be able to quickly rise and become popular. And yet they do. DashHopes is an example of someone who went from being unknown, to smashing the weekly leaderboard, very quickly - mostly from interacting with lots of other people with meme comments in a friendly way.
I think it looks like people upvote popular users rather than the meme, since popular users tend to on the front page more often than unknown users do. I think this happens (in part) because of the number of people who visit our profiles directly. Unknown users don't have that advantage, so it's harder for them to get a meme up the stream high enough where the imgflip community can get it to the front page (since nobody can upvote what they don't see). Unfortunately, a lot of good memes are overlooked on the site.
So yes, I can definitely see why you'd be thinking that. It's understandable. And being a popular user definitely has its advantages, but I don't think it's realistic that people's votes come from just one factor (e.g. popularity), without the content of the meme being a factor also.
Hope you don't mind the long comment.