For some people it may be easy. For others they may have awesome ideas but decide not to execute on those ideas because learning Arduino C++ or figuring out how to install Node on a RaspberryPi seems like a large barrier to entry for them. Maybe some of those people are those that make those awesome websites, and maybe with an embedded controller that feels more like the environment they're used to, they're more likely to bring their awesome ideas to fruition.
Disclaimer: I went to school with the Tessel folks.
Disclaimer: I went to school with the Tessel folks.