Relatively, they're correct. Compared to other app stores like Apple where the fee is $100/year, which personally I'd consider huge. To get on Steam, the fee is a one-time $100 with the ability to get it back after $1000 in sales. It's even low compared to Google's other marketplace, the Play Store, which has a $25 one-time fee.

While $5 can be a lot for certain people, relative to the market it doesn't deserve the title of being "huge".