Yes they are, you read it here first.
I bought an arm wallet while I was in Vegas last year, and it's been great. I wear it, unsurprisingly, while running, and I keep stuff in it. Key, lip balm, Kendal Mint Cake, that kind of stuff. I had thought that I had perhaps picked up a child's size as I can't even get the fucker past my elbow; perhaps a woman's size, I don't know.
Turns out no, it's a one-size-fits-all. It also turns out that what I thought were fairly normal sized arms, aren't. I know I'm strong and everything, but mostly that's through the shoulders and legs. Well, turns out my arms are apparently fucking huge, because I tried on an arm wallet today, one for a smartphone or similar, and it just didn't work. It was at least an inch away from the Velcro even touching slightly when it was on my bicep.
Of course, this means I am incredibly manly and everything, which is good. But it also means arm wallets stay on my forearm only, which is… annoying.
So, to summarize, arm wallets are all bastards. That is all.