Apparently one of the projects listed, Packery, is licensed under the MIT license for open source projects, and under an expensive commercial license for commercial projects. This makes my brain hurt. Isn't the whole point of the MIT license that it can be sublicensed without restriction? Then what's to stop someone from sublicensing the free version to themselves for commercial use?
I'll admit the license issue is weird, but really–since when is $25 or $90 expensive?
I purchased the Isotope commercial license a few months back and I actually bought the Packery one today. I'm not really concerned with the nuances or semantics of the licensing.
I'm not sure about the MIT, but I believe nothing stops them from doing that. It's like WordPress themes or plugins licensed under the GPL. Most of the time, you pay for support and additional features.
If you license under MIT but restrict who can use the software, it's not really MIT. MIT explicitly states that you may use the software "without restriction".
The GPL is even more stringent in that it doesn't allow you to further restrict the usage of others.
It's less about the cost and more about the fact that they don't understand open source licensing.
http://packery.metafizzy.co/license.html